Migrate to Gtk3 and GObject introspection.

* Applied Joanie's GTK fix and fixed camera issue.
* Update handler.py
* Merged Nikki's fixes for window and button sizes
* Fixed size of main window and Preff Buttons
* Updated files for deprecations of Gtk.HBox, Gtk.VBox, and Gtk.HButtonBox
* fixed Gtk.Table deprecation
* Fix GdkPixbuf.InterpType typo.