Canvas is invisible to the player until a username is accepted
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
Added some css to username fields
Merge branch 'usernameInput' into development