Pre-roll slide editable for chat link

Eliminates need for editing Markdown file on-the-fly for changing chat link in pre-roll slide. Text styled as a hyperlink, editable in-browser for quick updating.

Screenshot:
![Screen Shot 2013-03-24 at 11 29 17 AM](https://f.cloud.github.com/assets/352082/295677/5ec03742-94a8-11e2-927d-85c099e3f6b8.png)