Add common tde_setup_msgfmt macro #18

To simplify the test for gettext and set msgfmt executable in each module, I have prepared a common macro tde_setup_msgfmt. Thanks to this, it will now be simple in each module:

if( BUILD_TRANSLATIONS )
  tde_setup_msgfmt( )
endif( )

With the automatic call tde_setup_msgfmt inside tde_create_translation, there is no need to call tde_setup_msgfmt separately in each module.

looks good!