Previously, userid was generated by the "/login" route and passed along.
This commit completely removes the uuid "userid" (and disables the LoginController too and any Jwt check).
"userid" is replaced by the "socket id" of the connection.
So a user is now identified using a socket id, which is unique for a given connection.
This PR adds the display of a circle around groups. This is useful to view where you need to go to speak to someone but also to debug.
Note: implementation is suboptimal, relying on a "graphics" object that is known to be slow. In the future, we need to use a circle as a sprite instead.
