DSFE3 Halt delivery

[AlexNi245]

When an account is not registered with DM3 yet. Messages that are about to be sent to that account should be stored in the Client storage to submit them as soon as the receiver has submitted their DM3 profile to ENS.

• [ ] There is a WebSocket called joined, which is fired when a new user joins the same DS as the recipient. This socket does not have a payload which makes it rather useless. It could however make sense to add the contact name as a payload so the client knows who has joined
• [ ] Figure out a way to know when a contract has been joined via ENS.
• [ ] Submit stored messages after the receiver has joined dm3