Release Version 0.15.4: Master of None

1. Port assignment for workers and frontend randomized and error checked to enable easy deployment of multiple instances make rebuild-dev command altered to skip frontend build. Perform these steps manually.
2. The Housekeeper now automatically updates URL's when repositories move. Consider this an alpha feature, but our testing to date shows robustness.
3. API Routes for Auggie, the slackbot, are added in the new API format.
4. API Development documentation substantially updated.
5. Frontend bug fixes. Last release got wonky again and we fixed that.
6. Schema update to ensure deletion of contributors is restricted. Contributor worker presently does not delete any users, but resolves canonical ones.
7. Added informational output to the installation scripts
8. Added two libraries to setup.py to support Slack API calls: boto3, and slack.
9. Gitlab issue worker patch: Now skips non-GitLab URL's entirely
10. Gitlab Merge Request worker patch: Now skips non-GitLab URL's entirely
11. Added debug logging to worker_base.py and pull_request_worker.py.