Don't notify when receiving own message from another device
Scenario:
- A uses Gajim and Conversations (on their mobile), both configured to use OMEMO
- B uses Conversations on their mobile
- A and B trust each other's OMEMO's keys, and use the protocol
When A sends a message to B from their mobile, A's Gajim will 1. popup a new window and 2. play a notification sound. As this is a message from A, neither is desirable (though the message should probably still be logged if Gajim is configured to do so).
Similarly, when B replies to A's message, Gajim will play a notification sound (popping the convo up is may or may not be fine there), even though A is currently using another device.
When Gajim knows it is the bystander of an OMEMO communication with another device, it should neither pop up nor play notification sounds when messages are received.
Conversations use some short timer after the last carbon-copied message from the owner's JID before assuming it is no longer a bystander. Gajim could probably do the same. I don't remember having had this issue with OTR, so perhaps something similar is already implemented there?