* Handle startSync and loadMore
* Use SyncManager rather than MailService for periodic sync
and upload sync
* First of many CL's to disentangle sync from UI
* Note that the large majority of this CL is a refactoring
of IMAP specific code out of MessagingController and into
ImapService; MessagingController will eventually be
removed entirely from the app, as will much of Controller
Change-Id: I13546d0694479b33cf93c25920dedc1d38227f6c
