transitions: Set fill parameters to False because they have no effect anyway
Use Gtk.Box instead of Gtk.VBox because Gtk.VBox is obsolete
elements: Fix padding argument for pack_start
Use Gtk.Box instead of Gtk.HBox because Gtk.HBox is obsolete
Fix spacing setting
clipproperties: Add the vbox directly to the ScrolledWindow

We depend on Gtk 3.10 and this is available since Gtk 3.8.