Fixes #448 missing live console output bug on rebuild

Hey there, I tried to fix the bug #448 with this commit. Since i looked today the first time at the codebase of this project, i am not 100% sure this is the correct solution.

The problem i saw was that when you force a rebuild, it gets stuck on:
server/pubsub/channel.go
```go
func (c *Channel) Subscribe() *Subscription {
	s := NewSubscription(c)
	c.subscribe <- s //<--- stuck here
	return s
}
```

because the Channel was only closed, but not removed.

When you issue a new rebuild, it well return the old channel. But since the start loop is not running anymore, `c.subscribe <- s` gets stuck because the value is not getting pulled out of the queue from the start() loop.

So now i unregister the channel at the end of the build instead of just closing it.

Hope this helps

Best regards

David