Bug 833291 - Part 2/7: add thread/participant stores.
Bug 833291 - Part 3/7: fix saveRecord().
Bug 833291 - Part 4/7: fix deleteMessage().
Bug 833291 - Part 5/7: fix markMessageRead().
Bug 833291 - Part 6/7: fix getThreadList().
Bug 833291 - Part 7/7: fix createMessageList().