[commhistory-daemon] Implement MmsHandler for receiving MMS messages

This connects with mms-engine via a custom D-Bus API to receive and
manage incoming MMS messages.
Show notifications for successfully received MMS
Merge pull request #42 from special/mms-listener

[commhistory-daemon] Implement initial MMS receive handling
[libcommhistory] Require mms-engine package
[commhistory-daemon] Handle MMS send/delivery state changes
[commhistory-daemon] Add MmsHandler::sendMessage dbus method

This method handles recording outgoing MMS events for commhistory,
storing message part files, and sending the actual MMS request to the
engine.