* UI changes in anticipation of polyglossia support:

* UI changes in anticipation of polyglossia support:
     - rename \language_package to \language_custom_package
     - the bool \language_use_babel is replaced by a more fine-grained selection:
        * chose language package automatically (later: babel or polyglossia)
        * always use babel (also with XeTeX)
        * custom (i.e. use \language_custom_package)
        * none (equivalent to former \language_use_babel false)

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@36407 a592a061-630c-0410-9148-cb99ea01b6c8