- changed periodic sync scheduling to just creating pending

  and changed the "get next operation to sync" logic just look
  at pending syncs, rather than them and periodic syncs
- made syncoperation dup-detection ignore the initialization
  sync extra
- made the sync dispatcher treat initialization syncs as just
  a regular sync request and also made it explicitly set or
  clear the initialization extra based on whether the sync
  adapter was in the syncable or unknown state
- change the getNextSync logic to prioritize syncable "unknown"
  syncs above everything else (since they should be fast and
  are important)
- make it reschedule completed initialization syncs if the
  sync adapter is now marked syncable
- fix some logging in SyncStorageEngine
- change SyncStorageEngine to not reuse authority ids when one
  is removed

http://b/issue?id=2531359
http://b/issue?id=2429638

Change-Id: I79805b582da74f4f0b6193eafaff24c2371d51e8