Issue #49 : Comments thread and submission form now support avatar disabling

Fix : issue #49 Hide avatars

To come along with this change, a few visual enhancements have been done :
* The avatar in the submission form now looks like it's indented inside the main textarea
* Clean and subtle separation lines between each comment have been added

**With the avatars on :**
![2014-05-22-200316_657x834_scrot](https://cloud.githubusercontent.com/assets/914451/3056587/308d9b90-e1cc-11e3-9fd5-8200d48e2d01.png)

**With the avatars off :**
![2014-05-22-200340_661x821_scrot](https://cloud.githubusercontent.com/assets/914451/3056591/3f09db84-e1cc-11e3-94e6-d744f6765bc8.png)