Added RefreshManager, which is responsible for getting refresh requests
from UI and keeping track of what is being refreshed.
Conceptually it's a part of Controller, but extracted for easier testing.
- Now sendPendingMessagesForAllAccounts() is owned by RefreshManager
rather than Controller.
- Also updateMailboxRefreshTime/mailboxRequiresRefresh have been moved
in from the Email class.
- Now MessagingException implements a method to return an error message
for the UI.
The refresh button on 2-pane doesn't work as intended yet, because the
spec is a bit too complicated (as described in the TODO in
MessageListXLFragmentManager.onRefhres()).
This change touches many file mostly because it cleans up a lot
of code duplication.
Change-Id: I058ab745ccff10f6e574f6ec4569c84ac4a3e10e
