Add support for CheckSuite API

[suprnova32]

GitHub recently introduced the CheckSuite API:

https://developer.github.com/changes/2018-05-07-new-checks-api-public-beta/
https://developer.github.com/v3/checks/

It would be perfect for AlloyCI to take advantage of this new feature. Even though inline comments might not be possible as of now, we could still take advantage of the other features, like re-triggering of jobs straight from GitHub, individual job statuses, better statuses, etc.

It would require to add functionality to Tentacat.