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's a good practice to use fewer commands where possible. Here you could collapse these four into one:

```
RUN mkdir -p /home/app/ihat && chown -R app /var/lib /usr/local/bin /home/
```

The reason is that [every command creates a new image](https://docs.docker.com/userguide/dockerimages/):

> We can see that each step creates a new container, runs the instruction inside that container and then commits that change

Also see [this post on StackOverflow](http://stackoverflow.com/questions/21467638/number-of-commands-in-dockerfile) for potential workarounds.