So far, someone joining a map would not see the circles of groups already formed until someone moves in the group (because the "circle_moved_or_updated" event was not fired when someone arrives)
This commit fixes this behaviour. Someone entering a room will receive an event for each and every group currently formed.
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.
