OTR: Add "otr-msg-event" enum in notification TpMessage's header
OTR: Add "otr-msg-event" enum in notification TpMessage's header

UI can use that to display a different/translated message.

Ziemin/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble