Create an issue when a tracked branch (with no PR) starts failing tests

[czechboy0]

Dependency: #18. Builds extra features on top of it.

Not just make Builda mark the commit appropriately on GitHub, also (optionally) create an issue if a watched branch suddenly starts failing tests (something like [Buildasaur]: Build failing on branch master) and comment what tests are failing exactly/what build error was emitted.
Then, when a new commit comes in that fails again, add a new comment with the new details (like we do with PRs).
Then, when a successful commit is pushed, comment that the issue was resolved and automatically close the issue.

• Add functionality to:
• Get open Issues
• Create a new issue
• Close an issue
• Add logic for creating the Issue when a tracked branch fails, mark the issue with a special label so that we can then only fetch these ones instead of all open Issues (reference 1, reference 2)
• Add logic for finding an existing matching issue (pull all open Issues with the special label first), create one if none exists
• Make sure the PR logic for only posting a comment if it hasn't done so etc is working
• Add logic for closing the Issue when the branch succeeds again