selection-canvas-item: use GdkFrameClock for rubberband animation

Make it a bit smoother.
view: remove "menus_are_untrustworthy" boolean flag from NautilusView

It doesn't seem to do anything really useful.
Fix Close Window accelerator

Commit 032f37f49778c1b8214b88b764ac29c1654b12e0 removed the action from
the menu, but won't keep the accelerator unless explicitly specified in
the XML file; add it in the XML file so Ctrl+w works.