Add Dockerfile

[erikvold]

Adding a Dockerfile would allow us to easily run tests in a container instead of on our host computer (to protect against instances like this one with eslint), and also allows someone that might have a platform issue running the build and/or tests on their host computer then they will still easily be able to run our npm scripts with docker, also I think this will help us with testing by providing easy access to another platform for us to test on (for example we can pretty closely reproduce the results that CircleCI might have which we don't get on our dev computer).