Set up Dockerfile to ease development environment setup

[nikolas]

The 3demos tech stack could more easily be pre-configured using a Dockerfile or container comprising of the following setup:

• nginx
• Django
• redis

https://hub.docker.com/_/nginx

As an example, we have a basic Dockerfile setup for Mediathread here: https://github.com/ccnmtl/mediathread/blob/master/Dockerfile Though 3demos would be a bit different with our non-standard django setup.