Adds the remained of the conflict handling specification and is equivalent to
the Android code in how it selects different conflicts.

Adds CDTDatastore+Conflicts -resolveConflictsForDocument:resolver:error method

TD_Database+Conflicts was modified to return the same revisions as returned by
the Android library.

Adds CDTDatastore+Internal for CDTDatastore methods we wish to keep private.
* moved CDTDatastore+Conflicts -conflictsForDocumentId to
  CDTDatastore+Internal activeRevisionsForDocumentId