Qt: Add Spanish (es) translation assets.

Add an initial "es" Qt translation file and an accompanying flag image.
The image came from

https://en.wikipedia.org/wiki/File:Flag_of_Spain.svg

and is in the public domain.

(We already had a debian/po/es.po.)

Change-Id: I5378ad2cbffb2267389fc8ae6af6d591071e0144
Reviewed-on: https://code.wireshark.org/review/35620
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>

.tx/config

@@ -6,6 +6,7 @@ file_filter = ui/qt/wireshark_<lang>.ts
 source_file = ui/qt/wireshark_en.ts
 source_lang = en
 trans.de = ui/qt/wireshark_de.ts
+trans.es = ui/qt/wireshark_es.ts
 trans.fr = ui/qt/wireshark_fr.ts
 trans.it = ui/qt/wireshark_it.ts
 trans.ja_JP = ui/qt/wireshark_ja_JP.ts

docbook/wsdg_src/WSDG_chapter_userinterface.adoc

@@ -200,6 +200,7 @@ translation, do the following:
 - Add your translation (_ui/qt/wireshark_XX.ts_) to _ui/qt/CMakeLists.txt_
 - (Recommended) Add a flag image for your language in _images/languages/XX.svg_. Update _image/languages/languages.qrc_ accordingly.
 - Run `lupdate ui/qt -ts ui/qt/wireshark_XX.ts` to generate/update your translation file.
+- Add ui/qt/wireshark_XX.ts to `.tx/config`.
 - Translate with Qt Linguist: `linguist ui/qt/wireshark_XX.ts`.
 - Do a test build and make sure the generated _wireshark_XX.qm_ binary file is included.
 - Push your translation to Gerrit for review. See <<ChSrcContribute>> for details.

image/languages/languages.qrc

@@ -2,6 +2,7 @@
     <qresource prefix="/languages">
         <file>de.svg</file>
         <file>en.svg</file>
+        <file>es.svg</file>
         <file>fr.svg</file>
         <file>it.svg</file>
         <file>ja_JP.svg</file>

ui/qt/CMakeLists.txt

@@ -579,6 +579,7 @@ endif()
 set(WIRESHARK_QT_TS
 	wireshark_de.ts
 	wireshark_en.ts # lupdate -pluralonly
+	wireshark_es.ts
 	wireshark_fr.ts
 	wireshark_it.ts
 	wireshark_ja_JP.ts