Switch to tablet style notification

- Now we show separate notification for each account
- New notification has sender photo, sender name, and subject
  of the latest email
- Added the NotificationController class, which is intended to manage
  all notifications besides "new message" eventually.

The framework doesn't seem to be 100% ready, and it's not clear how to
add the 3rd line in the expanded notification at this point.  Need to
revisit it later to verify UI details.

Change-Id: I40193ee372cb6b2b7245c1588890f238b2469699
3 files changed