add first radar prototype

Currently very buggy but it kind of works.

Current bugs:
- only player who opened server can see the radar
- other players don’t see their own radar, yet the player who opened
the server can see all of them
- as not all roles are recognized in the beginning, their radars remain
at the starting point until used. possible solutions: don’t start the
game (and the radar) until all 4 players joined - or hide radar, if
other players have not yet joined the game.