Byron/social buttons

Add "Follow" buttons for Twitter, FB, and Google+ on the About Page.
Add "Share" buttons for Twitter, FB, and Google+ on all Course Pages.

General Notes:
- not sure if I placed the buttons in the best places on the page
- would ideally have something like a "Follow Us" section in either the navbar or footer with cleaner/more uniform square icons (like http://zurb.com/playground/social-webicons)

Formatting Notes:
- awkward gaps between buttons
- fb button is slightly smaller and lower than twitter and google+ buttons
- all buttons do not respond nicely when screen is shrunk

Code Notes:
- code is kind of long
- Fb told me to "Include the JavaScript SDK on your page once, ideally right after the opening <body> tag." We might be able put this in base.html?