Configure: Improve GTK3 support
Add GTK3 support
copy-theme-dialog: Add GTK3 support
mate-screensaver-dialog: Add GTK3 support and fix GLIB deprecations
mate-screensaver-command: Fix glib deprecation
mate-screensaver-preferences: Add GTK3 support
test-fade: Add GTK3 support
savers: Add GTK3 support
floaters: Add GTK3 support
popsquares: Add GTK3 support
savers: Add GTK3 support