Add message in chat letting user know their message will be delivered

[SamPatt]

Currently if a user sends a chat message and the other user is offline, the message is stored in the DHT and will be delivered once the other user returns.

However, there's no indication to the sender that the other party isn't online and hasn't yet received the message. I suggest that if a message is sent to an offline user we display a little message saying "This message will be delivered once the user returns" or something to that effect.

@cpacia said this is possible but would require server changes. I'm making this low priority just so it doesn't get forgotten.

[jonathancross]

From the user's perspective, it would be much better if there was some kind of delivery status. Eg: in Signal, you see a single checkmark when the message is sent, then a second checkmark when it is received like so: