Implement #7341342 API request: way to determine current orientation...

...to allow for orientation locking

This doesn't add an API to get the current orientation, since that is
inherantly racy.  Instead there is a new "locked" orientation mode that
locks the screen into whatever the current rotation is.

While at it, added a few other useful orientation modes.

Change-Id: I5c369e6511cb72294e9e922ea8acffd770df9440