Resumable queries with sortkey

Gerrit allows resumable change list queries by passing in a "sortkey"
 associated with a given change, which is now saved and retreived from
 the database when making change list queries. The sortkey allows
 providing the server with the change we are up to regarding a given
 query.
GerritURL is parcelable so it can be stored in intents.
SyncProcessor now preserves the original GerritURL instance that was
 passed in.
Make the Status (or query) the primary key and usethe replace conflict
 algorithm.

Change-Id: I1adc924d7c6bd7be79077c2a423f6185923cfc10