HTML support for EAS 2.5 email

* Load MIME data for these messages and parse, looking for a body either
  in HTML or plain text or both
* If the MIME data had been trunctated and we can't find text, mark the
  message as partially loaded and load the body text as we did before
  (i.e. get the plain text body); this should be a rare case

TODO: Consider what is testable in the new EmailSyncAdapter code

Change-Id: I00a3066a373a0596431335593de356a4dda7f036
7 files changed