Add GitlabCI configuration
- Added our standard GitlabCI configuration
- Removed hardcoded versions of software, if we have constant CI we'll know when they break and why.
- Add Dockerfile for GitlabCI, to be able to execute the tests inside a container
- Add tox.sh to make the repo compatible with our standard GitlabCI config.
- Remove gunicorn from docker.txt requirements as it is already present in base.txt
Closes #37 (closed)