Update scope and add more config options

* Adds `user` scope because Github API now returns an empty array of orgs for a user unless it has the `user` scope.

* Add `hostname` config option to allow for setting callback hostname and being able to choose `https` vs. `http`.

* Add configurable `callbackPath` and `entryPath` in order to increase compatibility with other applications that may use Github OAuth for other purposes ([Drone](https://github.com/drone/drone))