Automated key exchange & user discovery

[ElementalMP4]

Add a feature to allow users to find eachother (contacts UI? account UI?) and exchange keys in order to become contacts. Implies that users know each other's names beforehand. Add a new websocket message type which will receive key exchange messages.

Also requires moving the websocket to a global scope instead of just the chat UI, and will require adding some kind of message subscription system so each view can hook into messages