Remove padding from <li> when used in Markdown

Fixes Markdown list items ending up looking like this:

![screenclip](https://f.cloud.github.com/assets/4501321/1814892/57fea5e4-6f07-11e3-8922-3db134ac622f.png)

Padding is preserved for party chat items overall, but when nested in a message, they should go line by line without padding, to reduce scrolling.