Dockerize iHat

REFERENCES
===
https://www.pivotaltracker.com/story/show/82965638

See the readme on the branch for installation instructions:

https://github.com/Tahi-project/iHat/blob/dockerize/README.md

TODO:

- [x] [Open URL on successful boot](https://github.com/Tahi-project/ihat/pull/27#discussion_r21470287)
It looks like `brew install fig` works too.