Qt: Add missing main menu mnemonics.

The GTK+ main menu had quite a few keyboard mnemonics which were missing
in the Qt UI, most notably File → Open, File → Close, and File → Quit.
Update ui/qt/main_window.ui from a list generated by running

`grep -E 'NULL, +".*_.*"' ui/gtk/main_menubar.c`

in a current master-2.6 checkout.

BTW, the proper terminology to use here is unclear. Most places use
"mnemonics":

GTK+: Access keys
https://developer.gnome.org/hig/stable/keyboard-input.html.en

Qt: Mnemonics or accelerator keys
http://doc.qt.io/qt-5/qkeysequence.html
http://doc.qt.io/qt-5/accelerators.html

Wikipedia: Mnemonics
https://en.wikipedia.org/wiki/Keyboard_shortcut

Windows: Menu access keys or mnemonics
https://docs.microsoft.com/en-us/windows/desktop/menurc/about-menus

Bug: 15475
Change-Id: Ibacbe066d4acfcea91125a980977d1610e3c0908
Reviewed-on: https://code.wireshark.org/review/31871
Reviewed-by: Gerald Combs <gerald@wireshark.org>
Petri-Dish: Gerald Combs <gerald@wireshark.org>
Tested-by: Petri Dish Buildbot
Reviewed-by: Anders Broman <a.broman58@gmail.com>

ui/qt/main_window.ui

@@ -153,7 +153,7 @@
     </property>
     <widget class="QMenu" name="menuOpenRecentCaptureFile">
      <property name="title">
-      <string>Open Recent</string>
+      <string>Open &amp;Recent</string>
      </property>
      <addaction name="actionDummyNoFilesFound"/>
     </widget>
@@ -311,7 +311,7 @@
     </widget>
     <widget class="QMenu" name="menuName_Resolution">
      <property name="title">
-      <string>Name Resolution</string>
+      <string>Name Resol&amp;ution</string>
      </property>
      <addaction name="actionViewEditResolvedName"/>
      <addaction name="separator"/>
@@ -525,7 +525,7 @@
     </widget>
     <widget class="QMenu" name="menuServiceResponseTime">
      <property name="title">
-      <string>Service Response Time</string>
+      <string>Service &amp;Response Time</string>
      </property>
     </widget>
     <addaction name="actionStatisticsCaptureFileProperties"/>
@@ -564,39 +564,39 @@
     </widget>
     <widget class="QMenu" name="menuRTP">
      <property name="title">
-      <string>RTP</string>
+      <string>&amp;RTP</string>
      </property>
      <addaction name="actionTelephonyRTPStreams"/>
      <addaction name="actionTelephonyRTPStreamAnalysis"/>
     </widget>
     <widget class="QMenu" name="menuTelephonySCTP">
      <property name="title">
-      <string>SCTP</string>
+      <string>S&amp;CTP</string>
      </property>
      <addaction name="actionSCTPAnalyseThisAssociation"/>
      <addaction name="actionSCTPShowAllAssociations"/>
     </widget>
     <widget class="QMenu" name="menuANSI">
      <property name="title">
-      <string>ANSI</string>
+      <string>&amp;ANSI</string>
      </property>
      <addaction name="actionTelephonyANSIPlaceholder"/>
     </widget>
     <widget class="QMenu" name="menuGSM">
      <property name="title">
-      <string>GSM</string>
+      <string>&amp;GSM</string>
      </property>
      <addaction name="actionTelephonyGSMPlaceholder"/>
     </widget>
     <widget class="QMenu" name="menuLTE">
      <property name="title">
-      <string>LTE</string>
+      <string>&amp;LTE</string>
      </property>
      <addaction name="actionTelephonyLTEPlaceholder"/>
     </widget>
     <widget class="QMenu" name="menuMTP3">
      <property name="title">
-      <string>MTP3</string>
+      <string>&amp;MTP3</string>
      </property>
      <addaction name="actionTelephonyMTP3Placeholder"/>
     </widget>
@@ -785,7 +785,7 @@
   </widget>
   <action name="actionFileOpen">
    <property name="text">
-    <string>Open</string>
+    <string>&amp;Open</string>
    </property>
    <property name="toolTip">
     <string>Open a capture file</string>
@@ -799,7 +799,7 @@
   </action>
   <action name="actionFileQuit">
    <property name="text">
-    <string>Quit</string>
+    <string>&amp;Quit</string>
    </property>
    <property name="toolTip">
     <string>Quit Wireshark</string>
@@ -838,7 +838,7 @@
   </action>
   <action name="actionFileClose">
    <property name="text">
-    <string>Close</string>
+    <string>&amp;Close</string>
    </property>
    <property name="toolTip">
     <string>Close this capture file</string>
@@ -1281,27 +1281,27 @@
   </action>
   <action name="actionFileExportAsCSV">
    <property name="text">
-    <string>As CSV…</string>
+    <string>As &amp;CSV…</string>
    </property>
   </action>
   <action name="actionFileExportAsCArrays">
    <property name="text">
-    <string>As &quot;C&quot; Arrays…</string>
+    <string>As &quot;C&quot; &amp;Arrays…</string>
    </property>
   </action>
   <action name="actionFileExportAsPSML">
    <property name="text">
-    <string>As PSML XML…</string>
+    <string>As P&amp;SML XML…</string>
    </property>
   </action>
   <action name="actionFileExportAsPDML">
    <property name="text">
-    <string>As PDML XML…</string>
+    <string>As P&amp;DML XML…</string>
    </property>
   </action>
   <action name="actionFileExportAsJSON">
    <property name="text">
-    <string>As JSON…</string>
+    <string>As &amp;JSON…</string>
    </property>
   </action>
   <action name="actionEditCopyDescription">
@@ -1453,7 +1453,7 @@
   </action>
   <action name="actionAnalyzeDisplayFilters">
    <property name="text">
-    <string>Display Filters…</string>
+    <string>Display &amp;Filters…</string>
    </property>
   </action>
   <action name="actionAnalyzeDisplayFilterMacros">
@@ -1529,7 +1529,7 @@
   </action>
   <action name="actionEditUnmarkAllDisplayed">
    <property name="text">
-    <string>Unmark All Displayed</string>
+    <string>&amp;Unmark All Displayed</string>
    </property>
    <property name="toolTip">
     <string>Unmark all displayed packets</string>
@@ -1587,7 +1587,7 @@
     <string>Unignore All Displayed</string>
    </property>
    <property name="toolTip">
-    <string>Unignore all displayed packets</string>
+    <string>U&amp;nignore all displayed packets</string>
    </property>
    <property name="shortcut">
     <string notr="true">Ctrl+Alt+D</string>
@@ -1672,7 +1672,7 @@
     <bool>false</bool>
    </property>
    <property name="text">
-    <string>Configuration Profiles…</string>
+    <string>&amp;Configuration Profiles…</string>
    </property>
    <property name="iconText">
     <string>Configuration profiles</string>
@@ -2151,7 +2151,7 @@
   </action>
   <action name="actionStatisticsConversations">
    <property name="text">
-    <string>Conversations</string>
+    <string>&amp;Conversations</string>
    </property>
    <property name="toolTip">
     <string>Conversations at different protocol levels</string>
@@ -2159,7 +2159,7 @@
   </action>
   <action name="actionStatisticsEndpoints">
    <property name="text">
-    <string>Endpoints</string>
+    <string>&amp;Endpoints</string>
    </property>
    <property name="toolTip">
     <string>Endpoints at different protocol levels</string>
@@ -2537,7 +2537,7 @@
   </action>
   <action name="actionViewInternalsConversationHashTables">
    <property name="text">
-    <string>Conversation Hash Tables</string>
+    <string>&amp;Conversation Hash Tables</string>
    </property>
    <property name="toolTip">
     <string>Show each conversation hash table</string>
@@ -2545,7 +2545,7 @@
   </action>
   <action name="actionViewInternalsDissectorTables">
    <property name="text">
-    <string>Dissector Tables</string>
+    <string>&amp;Dissector Tables</string>
    </property>
    <property name="toolTip">
     <string>Show each dissector table and its entries</string>
@@ -2553,7 +2553,7 @@
   </action>
   <action name="actionViewInternalsSupportedProtocols">
    <property name="text">
-    <string>Supported Protocols</string>
+    <string>&amp;Supported Protocols</string>
    </property>
    <property name="toolTip">
     <string>Show the currently supported protocols and display filter fields</string>
@@ -2585,7 +2585,7 @@
   </action>
   <action name="actionTelephonyLteRlcGraph">
    <property name="text">
-    <string>RLC Graph</string>
+    <string>RLC &amp;Graph</string>
    </property>
    <property name="toolTip">
     <string>LTE RLC graph</string>
@@ -2879,7 +2879,7 @@
   </action>
   <action name="actionTelephonyIax2StreamAnalysis">
    <property name="text">
-    <string>IAX2 Stream Analysis</string>
+    <string>IA&amp;X2 Stream Analysis</string>
    </property>
    <property name="toolTip">
     <string>IAX2 Stream Analysis</string>
@@ -2930,7 +2930,7 @@
   </action>
   <action name="actionGoGoToLinkedPacket">
    <property name="text">
-    <string>Go to Linked Packet</string>
+    <string>Go to &amp;Linked Packet</string>
    </property>
    <property name="toolTip">
     <string>Go to the packet referenced by the selected field.</string>