Initial submission for EAS support (email)

* There is some temporary code ensuring that SyncManager runs (this will be removed when Exchange
is entirely independent)
* The service interface (aidl) is in place for most user-facing actions (load more, start sync, etc.)
* EAS account validation is done via aidl
* Folder and message sync appear to be functional in this early submission
* Provider now does cascading deletes (Account -> HostAuth and Mailbox, Mailbox -> Message,
  Message -> Attachment and Body)
26 files changed