Add Dockerfile

[liam-middlebrook]

This adds a Dockerfile based build-environment container for Bingehack4. I've also made changes to the .drone.yml file to use the most recent image uploaded to Dockerhub (right now this is pointing to an image generated from my fork so that I won't have to change anything in-repo after it's merged in for CI to be happy)

Here's a log of Drone running before the change: https://drone.csh.rit.edu/liam-middlebrook/bingehack4/52/1

And here's a log of Drone running after the change: https://drone.csh.rit.edu/liam-middlebrook/bingehack4/56/1

As you can see there's roughly a 5x speedup for Drone after this change.

Fixes #76

[sdemos]

is there a particular reason you chose to use ubuntu as the base image? using alpine or something like that with a smaller footprint might be preferable.