Implement Google Analytics

We should implement Google Analytics into the UI so that we can measure user activity.

Ideally, we should send data for every action that the user undertakes. From logging in to browsing the tripos to logging out.
It's Monday you know... :)

![bkk63qqccaaddzp jpg-large](https://cloud.githubusercontent.com/assets/2194396/5434398/6ea2f82e-8449-11e4-827c-7c736346e3d5.jpeg)