CYB-41 Mock Data is fetched and shown on the Leaderboard

Added AngularJS leaderboard controller and factory, as well as integrated @ericayin 's front-end leaderboard html, css, and javascript code.
Leaderboard Factory fetches data from a url and displays on front-end
Also included some small style issues not covered in https://github.com/ets-berkeley-edu/datacultures/pull/3
HTTParty and Canvas_lti_controller changes are included to show how a Canvas API call can be made to return JSON

LeaderboardController.js is mostly commented out because it is not sprint specific
https://jira.ets.berkeley.edu/jira/browse/CYB-41
@NolanChan don't use `div.content`, use `.content` instead.
Actually, we should prefix all the classes in our code. e.g. `.dc-content`