Fix issue #38037532: Toasts cause apps to become foreground

ForegroundToken is now ImportanceToken, and doesn't actually
cause an app to become foreground (that is not needed for
toasts anyway).

Also improved output and logging -- new logs for changing
in key uid stats, and when force stopping services after a
uid goes idle.

Test: manual

Change-Id: I44dd391bb8d37857be1359f4b7021dc8d2cd0285