pull request to include json icon for new file upload 

Adding blank icon as well for future file types.
![json-file](https://f.cloud.github.com/assets/282682/314835/4428836e-97d5-11e2-87f6-a7c462e890dc.png)
![blank-file](https://f.cloud.github.com/assets/282682/314836/4918dc48-97d5-11e2-8f3e-4d031073be02.png)