Improved GitHub and Bitbucket build status messages

If you have a private project linked with a GitHub or Bitbucket repository you probably noticed that codebeat posts build statuses on Pull Requests to the tracked branch. We used to base these on project GPA. If the total project score decreased as a result of PR change, you'd get a failing status. This was in principle a good idea but in practice it was unlikely that in larger projects a given Pull Request would change the GPA, so most of the commit status messages we were showing were more or less useless.

We decided to change the logic to look at the number of issues resolved and introduced by a given Pull Request. If the number of new problems is larger than the number of problems addressed, we'll send a failing status. With this new scheme an issue is an issue is an issue, so it is possible (although not that likely) that introducing one serious issue that moves the GPA down while addressing two insignificant ones will still yield a green build. As someone once said, life is a series of trade-offs.