Add vty and logging previously used from libcommon
Rename libmgcp to libosmo-legacy-mgcp and install.
Use DLMGCP, not DMGCP.
Slim down the public mgcpgw_client API, move all elements not actually used by
current callers to private headers / static c.
Depends: libosmocore I09c587e2d59472cbde852d467d457254746d9e67
Change-Id: I71a0a16ebaaef881c34235849601fc40aa12cfd7
Neels Hofmeyr