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
:clap: Nice work abstracting these out - do we need to give any heads up to the open source community for theming purposes that these have been made or will override any of their business?