horizon-manage.py provides a module option to define different project
modules (horizon modules are default), so provide this option also here
Compile messages can be perform directly in horizon_lib_dir.
It's not required to go in each module dir, so removed this.
All messages will compiled now which takes insignificantly longer.
Change-Id: I82be90e722780d27bb0593575b8bfe5befe46686
066e462c64