gtk spell user experience is not in a good state

First of all, if I enable highlighting then the default lang should be checked in every popupmenu. And I speak about http://trac.gajim.org/changeset/6711

Moreover, the minute we enable we should check if we have spell dict for the default lang, and if not, we should inform the user (already there for when we init a new textview) and uncheck it from prefs. All this on the fly in Prefs Window