Added a dialog that shows when app has not been authorized by
DevicePolicyManager.isLockTaskAuthorized. This allows any app
to trigger lock-to-app mode. This same dialog is used when
startLockTaskOnCurrent is triggered by the recents long-press.
Can exit the mode by long-pressing recents again.
Keyguard is disabled when lock-to-app is active.
This CL also prevents apps from finishing when they are the root
task in a lock task TaskRecord.
Change-Id: Ib54d858e570cccf6bfd986958868e15f49bcef75
62515beee6