Fix issue @16555033: Battery history overflowing too much

- No longer track process starts/stops normally.
- Increase buffer size to 256KB.
- Buffer size increase requires reworking how battery stats
  are retrieved, since it is going to be hitting IPC limits.
- Also, store the last full stats after a reset, to be reported
  at the next checkin.
- Also, discharge and charge times are tagged with the screen
  and battery save state during that time.

Change-Id: Ie108ac9b626846108a9bb858101ac2b93276ac16