Changed module containers to Gtk.Grid.
Added Gtk.Grid to tab containers.
Updated cs_default.py layout.
Removed lock_widths.
Replaced lock_width with grid_align.
Simplified Adjustment.py.
Removed Affix.py widget.
Changed InputWidgets' descendants' class inheritance order, fixes MRO for set_* methods.
Removed some test code from Background.py.
Hooked CSW.CheckButton's label's click event to toggle the button's state.
Restructured the way CSW.Container adds widgets.
Added set_margin_left/right() to InputWidget.
Updated CSW.FontButton and CSW.Range/Scale to use the new InputWidget template.