Improve two-column CSS

The `two-wide` system causes problems if there are an odd number of columns,
so use floats and `width: 50%` instead. Also changed `box-sizing` so padding
is calculated more predictably.

The 480px stylesheet was only in charge of eliminating the effect of the
`two-pair` wrapping div, it had no other purpose. So it has been removed.
Add 'Wins' item type.

* Labs is amazing. We should celebrate our wins more. This change aims to give
  people a well-defined venue to tell their peers about their successes, let
  us all applaud, and give everyone a nice high point to start their day.

* It is last in the list of standup items to give everyone a happy point to
  start their day on. I intend for the tradition to be a brief round of
  applause for each win.

* Tweaked subtitles a bit. Hopefully will help people understand what to use
  Wins for.
Skip Wins at the end if there aren't any
Merge pull request #67 from thecadams/add_wins

Add wins event type to Whiteboard