Handle \textgreek commands from unicodesymbols

This is the second part of bug #8553: The symbols defined in unicodesymbols
are now detected correctly and converted to unicode, so no ERT anymore.
Parse post command argument insets (bug #8473)

This is now very easy with the new InsetArgument infrastructure.
Parse tikzpicture env. correctly (bug #9011)
Merge remote-tracking branch 'github/build-bot-master' into bleeding-edge-master
2014.12.30-18.00