Add ability to change retro passwords

[davidje13]

Changing the password should also cycle the retro auth keys and force all connections to the retro to close immediately with 4403. This will cause all tokens to become invalid, and prompt a re-authentication flow for the users.

The user changing the password should be re-authenticated automatically. Other users should be prompted for the new password.

Might be best to handle this through a new API rather than through the WebSockets.

Depends on #4 for automatic re-authentication flow.