Add basic backbone views

This adds some backbone stuff (in `/assets/js/backbone.js`) that does the following:

1. On page load, instantiate a Backbone router which fetches `/api/candidates` into a Backbone collection of Backbone models.
2. When the /api/candidates returns results, pass the Backbone collection of candidates in to a Backbone view which is responsible for rendering the overview table
3. The backbone view immediately renders the overview table.