Introduce controller for transcode notifications

This is to provider users with control over whether to show transcoding
notifications or not.

By default we show the notifications.

The controller resides within the Media transcoding settings under
Developer Options.

BUG: 170973510
Test: manual. unit test added.
Change-Id: I7172f583ce4c1a53e5d5ccc07625f201852db43a
3 files changed