Stability improvement

Upload of too big files - previously 2m, currently 20m - lead to unhandled exception.

• changed version style to pep40 but added another geoconvversion option to output version directly usable as docker image tag
• number of workers is configurable now

Performance improvements

• Using gunicorn as production service handler which should be much better than just using runserver.
• Version and date will now be generated dynamically