Github refactor

This is a refactor of our github monitor to separate it into different monitors for different things. This means we can run them at different rates. It also now uses Github OAuth, vastly increasing the rate limit, and cleans up the VCR cassette naming.

It will required changes to the schedule in services-manager when integrated into that, and adds a new GITHUB_OAUTH_TOKEN environment variable (the correct value of which can be obtained from me or Jenkins, currently).