vrwm: Add 2D Mode + control app change

2D mode is similar to debug mode in that it will always show the
application layer if it exists, but unlike debug mode will strip any
system layers from the output and will attempt to recognize the VR
layers. The virtual display is always in 2D mode as it can only show
2D apps. The primary display can be switched by vr_wm_ctl

Bug: None
Test: Manual with permissionsgen and launching calculator app
Change-Id: I38d025c457b1fca9aeb47cb94ed481ac9ff084f9