App Standby : Association between content providers and their sync adapter

Set sync adapters to active if the associated content providers are used
at foreground process state.

Minimize how frequently published content providers are reported by
keeping track of last reported time.

Also cache sync adapters associated with an authority in SyncManager.

Bug: 21785111
Change-Id: Ic2c8cb6a27f005d1a1d0aad21d36b1510160753a