Create Counter tool

[Ishadijcks]

The Counter should take an interval in seconds. After running update(delta) on it, it can be used in 3 ways:

const c = new Counter(30, this.save)
c.update(delta)

const c = new Counter(30)
c.onComplete.subscribe(this.save)

const c = new Counter(30)
if(c.update(delta)) {
    this.save()
}

This Counter should replace the save interval, achievement check and special events

Also add a boolean that determines if excess delta should carry over or be discarded