Fix delay sending stuck mail after tapping "Send outgoing mail"

* Fixes #2317429
* When "Send outgoing messages" is tapped in Outbox MessageList view,
  we clear the error state for all "stuck" messages
* We didn't, however, clear the error state of the Mailbox, which doesn't
  clear itself until the end of a pingLoop, which can be up to 30 minutes
* The fix is in two parts:
  * We clear the error state of the Outbox when a sync is requested by
    the UI
  * We don't set the error state of the mailbox for non-auth errors when
    sending, because we don't want to block OTHER messages from getting sent.

Change-Id: I768138b6f31eb696811aa94f621b6fa758ec1a5e
2 files changed