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 also removed "(Using "lighten" and "darken") functions is encouraged however." because I haven't used any of them, lighten and darken is good for getting colors automatically but I prefer to pick the colors individually because numbers can lie when it comes to colors; it's better to see them in context.