Make consistent ordering for lists from PatchLineCommentsUtil

Change-Id: Ia6ae44f387444a29b259ce02166aade808bf70c0
Create RebuildNoteDb to migrate data from ReviewDb to notedb

RebuildNotedb is responsible for the migration of pre-existing changes in
the ReviewDb to the notedb. It asynchronously rebuilds every change in
the ReviewDb and all of the related pieces of metadata that can be
stored in the notedb (i.e. PatchSets and PatchSetApprovals). As we add
the ability to store more data in the notedb, this can be updated to
migrate that data as well.

Change-Id: If0fb123630a08ef514611944e7bd0ab1d9e48f80