Adding option to show Disqus comments on click

This option adds the ability to show Disqus comments when the user clicks a button (Join the Discussion). The button needs some styling and the text will need to be translated, though. Other than that, this works the way you'd expect.

![screen shot 2014-04-29 at 5 17 10 pm](https://cloud.githubusercontent.com/assets/414475/2835007/c1d77c7e-cfe3-11e3-97f3-63a0f7836aaa.png)
![screen shot 2014-04-29 at 5 17 38 pm](https://cloud.githubusercontent.com/assets/414475/2835008/c1d84262-cfe3-11e3-8366-73e5002dd9c3.png)