allow sync adapter authors to control more policies

- let the SyncManager know that the SyncAdapter can handle
  parallel syncs even within sync adapter types
- allow indicating that the sync adapter should be auto
  initialized without requiring the sync adapter to run first.
  When this setting is used then setIsSyncable(1) is automatically
  called for the sync adapter.

Change-Id: Ib40eba95c2556eaee4bb0fe715f379af1b72b84a