Start implementing background restrictions for eph apps.

This implements the additional intended path for checking
allowed background operations, APP_START_MODE_DISABLED, which
doesn't allow an app to launch in the background at all.

Also change the semantics of delivering broadcasts to manifest
receivers to always restrict those, not changing based on
whether the app is currently idle.  This is the desired intended
behavior for apps as they explicitly update to work with
bg check.

And now that we have ephemerality associated with the uid state
in the activity manager, we can propagate this through the
relevant callbacks in IUidObserver so things watching these
changes can immediately determine whether they should do their
more aggressive shut down work for the uid rather than having
to walk through all their state looking for package associated
with that uid and whether they should be shut down.

Also remove the "lenient" bg check mode, since that was
just an early experiment that we won't actually use.

Add a new "make-idle" activity manager command to immediately
put a uid into the idle state (if possible) to make it easier
to test.

Test: manually against an eph app
Change-Id: I43a138ff281f69a9251d3f29ab6e13f48cff8ad6