[WIP] PoC - add Docker for Monofony

[gabiudrescu]

Fixes #193

What I did:

• I took the docker configuration from SyliusStandard and adapted it to Monofony
• improved it to match some of my requirements, such as:
  -- not running containers as root
  -- solved some caching issues with docker and docker-compose by using a scratch container to have a copy of all files from context
  -- added redis to be able to use same session from multiple containers
  -- switched the hardcoded locale to an env parameter

Still to do:

• add documentation done
• add ability to run testing suite from containers decided not to tackle this now
• add gitlab-ci.yml to allow ci on gitlab done
• move docker registry to dockerhub done

[gabiudrescu]

I did this PR because I wanted to start working on #238 and I realized that I don't have a working environment on my laptop. And since I created a Docker setup for me, I thought it would be nice to submit it here as well.