Now that all panels have been ported, we no longer need to do g_type_ensure. https://bugzilla.gnome.org/show_bug.cgi?id=702164
This promotes better encapsulation and allows us to move application logic out of main() and rename the confusingly named control-center.c to main.c https://bugzilla.gnome.org/show_bug.cgi?id=692174