I added the Dockerfile for the future Django application. It's based on
the rails Dockerfile with the following tweaks:

- Installation of Python 3 and pip
- Edit of the Python symbolic link to force the use of Python 3 by
default

I decided to store the app in the same folder as the rails app was as
they are not meant to work side by side. It will also facilitate the
debugging for developpers who were working on the rails app. If they
need to look into it for debbugging reasons, the path where to find it
is still the same.

Signed-off-by: Matthieu Berjon <matthieu.berjon@inria.fr>