Implemented Docker into the application

Changes made:

Added a Dockerfile and compose.yaml file such that the project can be compiled into a Docker image using Docker Desktop/Docker Engine + Compose
Added a .dockerignore file to exclude sensitive data (.env) and various unneeded cache files
- .env SECRET_KEY is declared as an environment variable in compose.yaml, so the app's auth system should still work when running the app through an image
Updated the README in app/ to remove any instructions on virtualenv and add in Docker setup info (since with Docker, virtualenv is basically redundant)

General Notes/Comments:

I'm not exactly sure whether if I set up the volume correctly in the yaml file, or whether if it's even necessary to have; any feedback on this would be greatly appreciated.
Running the Docker application will obviously require you to install Docker Desktop/Engine itself on your local machine; refer to the updated README for further instructions (provided that the steps themselves are accurate).
If there's anything else missing that I should implement within/alongside the Dockerfile and .yaml file, please let me know.

DSC-McMaster-U / Gamified-Learning-Platform