Add dockerfile and docker compose file

[grenaad]

• Adds a Dockerfile to easily compile and run the server on any platform.
• Adds docker-compose to make starting the server as easy as: docker-compose up -d

You can also add a reference to docker hub to make starting the server even more convenient

Reference issues: #66

[ja2142]

Docker container would be great, but I think it'd better to:

• make it from local files instead of installing git,
• use a production server.

Here's what I came up with:

FROM frolvlad/alpine-python3:latest

WORKDIR /app

ADD . /app
RUN pip3 install gunicorn
RUN pip3 install -e .

EXPOSE 8080

ENTRYPOINT ["gunicorn", "--bind", "0.0.0.0:8080", "youtube_dl_server.app:app"]

Though, at this point I doubt owner of this repo will merge anything...