Added the ability to post to Facebook

The “Update Social Media” button position/styling is far from final,
but I just wanted to get everything hooked up :).

Note that due to the way Facebook permissions work, social media
posting will only work with test users until we have requested
permission from Facebook to post to users’ walls. (This will have to be
done after deployment)

If you want to test the posting in the meantime, use the following
account:

Email: ywqaujd_rosenthalescu_1412740265@tfbnw.net
Password: asdf