Add a scrim to AllApps and Widgets

Check the size of the scrim and draw on the bottom of AllApps and Widgets.
Add a padding to the bottom of AllApps and Widgets so content is above the scrim.
Change the color of nav buttons for better accessibility.
Correct width of the Widgets sheets to be the same as AllApps sheet.

Fixes: 221107977
Fixes: 214215594
Test: manual, HSV and Window
Change-Id: Ib7510ffcd80231de7fefcdef65b422174dd74593