Dockerize!

This turned out to be easier than expected. Assuming users only interact with Mimic through the REST API, this is sufficient.

I added documentation on how to use this to the README. I figured you would probably want to keep the existing instructions as the default.
1. It starts with Debian jessie with [buildpack-deps](https://registry.hub.docker.com/_/buildpack-deps/). This is basically just jessie + a lot of the dev headers you probably want (stuff like libssl-dev) + build-essentials. [Details here](https://github.com/docker-library/buildpack-deps/blob/master/jessie/Dockerfile).
1. Then, [it installs python from a tarball off of python.org](https://github.com/docker-library/python/blob/a30ed3056ee58ca3df4fd5b51e3d30849dcb7e32/2.7/Dockerfile#L13).
1. Then, [it (globally) installs requirements.txt](https://github.com/docker-library/python/blob/a30ed3056ee58ca3df4fd5b51e3d30849dcb7e32/2.7/onbuild/Dockerfile).

This has two unfortunate potential security problems:

1. It runs mimic as root (granted, inside a container, but that isnt' actually necessary).
2. It leaves an entire buildchain lying around, e.g.:

```
[~] docker run -it mimic which gcc
/usr/bin/gcc
```

Given mimic's testing-only nature this probably isn't the worst, but I guess it would still be nice to fix those things. I'll see what I can do.