Fixes to idle alarm scheduling, package importance.

- Add new API to ask the activity manager what the current
  importance of a particular package name is (along with a few
  new useful importance levels).

- Fix my last alarm manager change to actually execute the
  alarms we have now decided should run even while we are idle.

Change-Id: I1f14712b4e390770d53b185c96a1b36f6aadd687