Add initial Backbone guidelines

Conventions in the Backbone.js community:

http://ricostacruz.com/backbone-patterns/#conventions
https://learn.thoughtbot.com/products/1-backbone-js-on-rails
https://learn.thoughtbot.com/workshops/22-hands-on-backbone-js-on-rails

The common alternative naming convention `App.Models.Photo` /
`App.Collections.Photos` / `App.Views.Photo` is unnecessary in Asynchronous
Module Definition-style projects using a library like RequireJS.

http://requirejs.org/docs/whyamd.html