If player joins; a ball is added to the mainscreen

Not yet client-sided, so shield collisions doesn’t work yet.
Fixed error on main screen

At first the balls aren’t initialized yet, so balls.getMember(index) in
the drawBall listener threw an error in that case.
Clients can see multiple balls now

Just see, movement is still not very good (some balls just hang, others
move around a little bit)
Changed label color and fixed more balls on client screen

Only problem is; it doesn’t work as playergame.js is fired long after
the balls have to be added. Someone any idea from where playergame.js
is called?
Merge branch 'extra_ball' into serverOverhaul