Show unread count momentarily in subtitle

Using new UX: Changing the account name to the unread count.

1. Show the unread count when the folder/account changes.
2. Unread count persists for 5 seconds.
3. On updates, it is shown again. (Unless the user had 999+
   unread messages, and the new count is also 999+)

Bug: 8556913 I have 999+ problem emails, and I just don't care
Change-Id: Iba8bcf2f5e51ae15fd9144bf790ccc419a533c8f
4 files changed