Re-design forum thread list and add labels

There are currently two significant differences from the mockup:
1. The contents of each item are vertically aligned to the top instead of the middle.
2. The comments icon is always blue for unread comments (whereas in the mockup it is blue for an unread post or white with a blue border for a read post with unread comments).

@jimabramson @talbs @marcotuts 

FYI @aboudreault @antoviaque
lost the thread where you mentioned using a CSS generated element/shape that can pull from the same Sass color variable for this. I'm all in favor of that rather than a rasterized image. This generator (http://apps.eky.hk/css-triangle-generator/) may be of help.