some changes due to an API review

 - make EntityIterator extend Iterator and thus not throw a
   RemoteException, instead converting it into a RuntimeException.
 - rename ActiveSyncInfo to SyncInfo
 - change getActiveSync to getCurrentSync
 - remove the accessors in SyncInfo and instead make the final
   fields publicly accessible

Change-Id: Id67bc22b34f3c0d8bf59a70c38c2e4622dd83e29
http://b/issue?id=2553539
http://b/issue?id=2553541