Overscan improvement: all apps extend to overscan area.

Introduce another new rectangle in window layout, the
restricted overscan region.  This is for windows that can
be in the restricted region (that is, full screen but with
hard restrictions like the nav bar) but whose content can
be adjusted for the overscan constraints.

In other words, normal application windows now always extend
into the overscan region, and we push their content inside
of it.

Change-Id: Ibccf3d7f144912d49de3fc497c1ec2e8e0b7f714