GanttCalendarPlugin: fixed a `KeyError` if locale directory doesn't exist, e.g. egg file built without Babel

git-svn-id: http://svn.sourceforge.jp/svnroot/shibuya-trac/plugins/ganttcalendarplugin/trunk@852 456a77e7-5939-0410-b211-84f85430c667
GanttCalendarPlugin: removed compiled message catalogs

git-svn-id: http://svn.sourceforge.jp/svnroot/shibuya-trac/plugins/ganttcalendarplugin/trunk@853 456a77e7-5939-0410-b211-84f85430c667