User restriction for disallowing window creation

Block any types of windows that could by used by apps to create
views on top of a locked app.  This can be used by device admins
in conjunction with lock task mode.

Added a way for system (and priv apps) to bypass user restrictions
for specified op codes.

Bug: 15279535
Change-Id: I2381530ef6226a5bb32a99bb4030baafb39bf564