6706: update POTFILES.in POTFILES.skip

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@22210 4ae1f11a-8b86-4847-b8af-ab372f36d1fd
6706: some translation messages were missing, update template, add better comments on POTFILES.skip

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@22213 4ae1f11a-8b86-4847-b8af-ab372f36d1fd