[commhistory-daemon] Always mark outgoing MMS message events as seen

The isRead property refers to whether the user has seen an event, for
inbound events. An outgoing event shouldn't be considered unread.

There is a different property for remote read state when read receipts
are enabled.
Merge pull request #46 from special/mms-sent-isread

[commhistory-daemon] Always mark outgoing MMS message events as seen