Add Screen pinning back to settings

Adds a basic screen for screen pinning (previously lock-to-app) to
settings that describes the feature and allows it to be turned on
and off.

Bug: 16378448
Depends on Ide333463f86310eacb7a1d8b6dc7b1aea8722713 for Settings
constant
Change-Id: Id3ef8471794aa01de20efeb947bed95c50d6b954