Don't build Docker image using docker-compose

Ghost User
2020-02-19T21:50:24+01:00

### Short description
Do not use `docker-compose` to build the Docker image.

This removes the need for the (very outdated) [`thalia/docker-compose` image](https://hub.docker.com/r/thalia/docker-compose) and [thaliawww/docker-dockerco...