Fix problem with timeouts and sending attachments (#2178288)

* Standard Exchange command timeouts are 20 seconds
* For sending, however, these need to be significantly longer to
  handle the case of sending large attachments, as sending (of any
  length) happens in a single HTTP Post command
* Having an infinite timeout leads to the (small) possibility of the
  Outbox hanging for a long time, holding up the sending of other
  mail, so we set a long, but not infinite timeout for this case
* Timeout now set for 15 minutes
* Prevent sync of Outbox and Drafts (the UI triggers these by changing
  the contents of these boxes, but we need to ignore the pings that
  are generated this way)

Change-Id: I5b830d6b4e94525d95138b2112be12898a37882e
3 files changed