Fix issue #15681802: Missing RESET:TIME in complete battery histories

But wait, there's more!

- Keep track of sync durations in the aggregated stats.
- Add events for users that are running and in the foreground.
- Rework the activity manager's tracking of stuff using
  battery in the background to be based on proc stats, which
  allows it to be better about determing when it should reset
  its tracking of background work.
- Also add tracking of scheduled job execution, like we are
  doing for syncs.
- And once I started hooking battery stats in to
  JobSchedulerService, I found a few things I couldn't stop myself
  from changing: (1) make it very explicit that it doesn't start
  scheduling jobs until we have reached the point in system boot
  where third party apps are allowed to run, and (2) adjust
  the various for loops to not use iterators.

Change-Id: I69d812e27bcfee9e58a614f0f6b1c7545d7530b1