Improve message counting, ah ah ah!

- Restore message_count in the database.
- For UI queries on outbox, trash, and drafts,
  use message count instead of total count.

Note this won't be the right thing to do when we properly
sync trash & drafts, but we'll address that when those syncs
are fixed.

Bug: 10098601
Bug: 10113686
Change-Id: I647c74396ee12ed981d89bfb654cc6d0a25cac95
3 files changed