Add Docker script for one-line command deployment

This is slightly less instrusive than previous attempts to ease deployment.

On one hand, this is great because it encapsulate all heavy conversion binaries in one container.
On the other hand, it is not agnostic, clearly.

#### Notes

The ``.docker/run.sh`` is facultative. It's just a way to update the application with the last master version on container restart. Can be discussed.

Another option is to forget about software update, and just focus on running. Setting ``gunicorn`` as an entry point, whose default parameters would be ``--workers=4 production.ini``, this way :

```
ENTRYPOINT ["/opt/apps/convertit/bin/gunicorn_paster"]
CMD ["--workers=4", "/opt/apps/convertit/production.ini"]
```

http://crosbymichael.com/dockerfile-best-practices.html