* Refactor/simplify Transport/MailTransport
* Add serverCert column to HostAuth table in EmailProvider
* During first connection to server, save the server certificate
in the HostAuth; on subsequent connections, ensure that the
certificate presented has the same public key as the one
stored
* For now, we'll just fail to connect (with a CertificateException)
if there's a mismatch
TODO: Add some UI to handle different certificates
Bug: 6888866
Change-Id: Ia79497e89eaad8d43617b50d3771121b2ed7f687
7d5e2a7c08