- Removed "update-ui" signal, This signal was encouraging bad behaviour and too much
	    action on every project change.
	  - Removed glade_app_create_undo/redo_button().

	* gladeui/glade-project.c: Stop calling glade_app_update_ui ().

	* gladeui/glade-window.c:
	  - Listen to GladeProject::changed instead of update-ui and only update the
	    undo/redo actions when the active project changes.
	  - Remove the preview toolbutton
	  - Add tooltips to important actions

	* plugins/gtk+/gtk+.xml.in: Mark the "preview" action as "important" so it shows
	  up in the app toolbar automatically.