* Add intent filter for application/eml and message/rfc822 mime types,
launching MessageView with a Uri
* Modify loadMessageTask to handle the Uri by parsing the attachment's
input stream with Pop3Message.parse(), and then creating an
EmailProvider message in a special Mailbox created to hold
"attachment" messages
* Delete all "attachment" messages after the parent message is closed
* Add unit tests
Change-Id: I20276ee006b9f05b889f3c808d3dc407cde26d49
391ae25c43