Display the chat participants key fingerprint next to their username

[AlexITC]

Ideally, you should be able to see your own public key fingerprint and the room participants fingerprint.

This allow users to verify that the server is not doing a man-in-the-middle by swapping the public keys from the participants.

The frontend already has everything it needs, the required change is to hash the public keys to get a fingerprint which gets displayed in the UI.