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
 - made AbstractThreadedSyncAdapter.cancelSync not take a thread

Change-Id: I99fde5585bc5f1e95f4873ffbba189074a8d6372
http://b/issue?id=2553539
http://b/issue?id=2553541
http://b/issue?id=2553550