Discussion reply avatar

- User avatar for the top-level comment box:
![image](https://f.cloud.github.com/assets/960919/1910006/a264e942-7d0b-11e3-8978-f58b83fd0fd6.png)
- Styling response comment box and adding hide/show for parent comment:
![image](https://f.cloud.github.com/assets/960919/1910010/b7fc8170-7d0b-11e3-95f5-ed8f6c3fab23.png)
- Cancel button for top-level comment box
- Blockquote quick fix