Change control semantics in transcode settings

Change global transcode enable toggle preference to global disable
toggle preference. Change app slection for skipping transcode to
app selection for enabling transcode, by default transcoding would be
disabled for all apps.

Test: Manual, Roboelectric unit tests
Change-Id: I44f4d1b24fac70a4560e8b3a12d505bd2da26f20
5 files changed