Dark Core UI

https://trello.com/c/GjJNtQSX/1381-more-thorough-dark-mode

![screen shot 2014-08-11 at 9 51 56 pm](https://cloud.githubusercontent.com/assets/1495261/3886491/6af3f694-21dc-11e4-931a-fe45f0168e7e.png)

I wonder if I should remove those comments. Certain things are either theme agnostic (sidebar  black and white rgba values for highlights and shadows) or colors that'll probably only get used once and are the same color as other things by coincidence.