Support for Disqus added

Added the Disqus code snippet for Disqus comments for the theme. 
A textbox to enter the Disqus short name also shows up where the user can enter his shortname and voila, Disqus comments on their blog. 

If the field is left empty, then Disqus comments won't show up. 
![screen shot 2014-06-14 at 7 51 41 pm](https://cloud.githubusercontent.com/assets/915425/3278729/99ffa05e-f3cf-11e3-9581-73b94a83a76d.png)