title: How can I reject and close connections in django-channels 2?
body: <p>It's been 1 month since I started using django-channels and now I have a feeling that I am not disconnecting websockets properly.
  When I disconnect I want to destroy the group completely if no one is there and it should be no sign of existence.
  When I'm rejecting connections I raise channels.exceptions.DenyConnection or send {'accepted': 'False'}
  I was just wondering if this is the right way to do things that I've mentioned or not.</p>