Bug 826118 - [email/IMAP] Connection loss may not always result in error messages during synchronization, synchronization for the folder will break until app is restarted.

r? @mozsquib

https://bugzilla.mozilla.org/show_bug.cgi?id=826118

This is a continuation of @asutherland's pull request here:
https://github.com/mozilla-b2g/gaia-email-libs-and-more/pull/144

with an attempt to address [@mozsquib's API feedback](https://github.com/mozilla-b2g/gaia-email-libs-and-more/pull/144#discussion_r3348022). 

The diff from the original pull request is this commit in this pull request:
https://github.com/jrburke/gaia-email-libs-and-more/commit/460fc5bcc1f7c9a6cc5cf524d2cecefb00c10fd0

I may have misunderstood the guidance though, or just chosen bad API names. In which case I can start over if given more context.