Commandeer full screen user switcher for auto.

The full screen user switcher wasn't needed by the original
author so adapt it for the auto use case because it fits
really well. This change adds in some legal text (TBR - legal)
and tweaks the layout a bit.

Bug: 26559008
Change-Id: Ib78d0ec8a8d4ec8411dbbffe5852c5307c2cf42f