[commhistory-daemon] Show notifications for MMS errors

A notification should be shown any time a MMS event goes from an "active"
state to an "inactive" one. This adds notifications for MMS transfer errors
and cases where a manual download is required.

These notifications behave like and are grouped with other MMS related
notifications.
Merge pull request #53 from special/mms-notifications

[commhistory-daemon] Show notifications for MMS errors