This pull requests adds support to let map-machine run in a container. The added `Dockerfile` is a first running version, which has room for improvement, e.g. do not run the processes as root and use a virtual env, reduce image size by cleaning up apt cache. The `.dockerignore` ignores copying files to the container, which are not needed.
The docker build and an example call can look like this:
```
docker build -t strubbl_mapmachine .
docker run -v /data/mapmachine/maps:/maps strubbl_mapmachine render --cache /maps/cache -z 18 -o /maps/wentorf.svg -b 10.2445866411,53.4858307519,10.2726961915,53.4981753961
```
