Basic reload/import support
Intial full screen support

Unfortunately our pretty header bar is gone in full screen, so we'll
have to show new controls when this happens. Also we should group
video related controls together (follow up commit)
Use linked raised box for video controls
Add force-aspect-ratio button

Quite simply, aspect ratio is forced by default. Toggling the button
will then unforce it (which will usually look weird. Up to the user)
Hide toolbar after a delay in full screen mode