Gettext removed from master

[Vincent van Ravesteijn]

Dear all,

I just pushed a few commits that were developed by Jean-Marc (and me). 
From now on, LyX reads the po (gmo) files natively, which means we 
don't need gettext anymore. As this is quite an intrusive change, I want 
to inform you about it in this way.

Both autotools and CMake should be updated correctly. I tested this 
myself both on Windows and Linux before committing. Packagers on Windows 
(Uwe) and Mac (Stephan) probably will have to take some additional steps 
and update some scripts. Sorry for this.

Vincent