Update to support status based deployments

Right now this is subscribed to status and push events but only has code paths for handling push events. This does a few things.

* Creates deployments if status is checked and the incoming status is green.
* Removes the "deploy on push" button since that's implied.
* Update docs.

I started adding support for `contexts` here too, which will serve as a way to specify which ci contexts are required to create deployments(multiple-contexts).