Controls UI - Part 1 - Thumbnail support

Add dedicated support for displaying background images on
controls. Apply a basic scrim to the image as well as a shadow on the
status text in order to keep the text legible. More work is needed to
add a shadow to the icon.

Bug: 175200791
Test: manual, use Mock app with camera
Change-Id: Ib76704e6577d3335fc4a563280aa15429f9dd277