Bug 874405 - [email/IMAP] snippet/partial body fetch breaks on zero-length bodies. r=jrburke

landing https://github.com/mozilla-b2g/gaia-email-libs-and-more/pull/206
Enable storing application data along with a mail account.
Expose password through MailAccounts.
Pass MailAccounts to the callback in viewAccounts
Add support for push notifications.