There is no overview anymore -- Settings is always
visualizing a panel at any given time.
I just noticed that the Alt+Left shortcut was always
broken too. This will be fixed in a following commit.
These were only used by CcApplication, and at this level
of the program we don't need to use any wrapper functions,
since we're certain that the CcWindow is a GtkWindow subclass.
This commit updates the code to use the recently
introduced API. The new functions improve the
legibility and maintainability of the code, and
makes it easier to work on new features.
https://bugzilla.gnome.org/show_bug.cgi?id=766922
