Powerup timer is started on the server when the first player connects

Because of this, we won’t spam powerup messages every second when there
are 0 players (yes we did this). Also it stops creating new timers when
no players are left.
Moved addClient to sockethandler

So a client is now added after his username has been accepted (also
fixes inconsistent scores between player and server)
Removed console.log from servergame