Displaying circle on join

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.

back/src/Model/World.ts

@@ -43,6 +43,10 @@ export class World {
         this.groupDeletedCallback = groupDeletedCallback;
     }
 
+    public getGroups(): Group[] {
+        return this.groups;
+    }
+
     public join(userPosition: MessageUserPosition): void {
         this.users.set(userPosition.userId, {
             id: userPosition.userId,