UI Tweaks, Layout and theming.

This commit covers a couple things:

- Fixes column layout with simpler markup and clearfix
- Adds a filename that links to the mistakes.io version
- Adds a Mistakes attribution that links to about
- A minimal light theme

My feeling was that the buttons at the top linked to too many of the 
same places. The goal of the filename was the ability to link to the full screen 
version and that it would be helpful to see the name of the file when embedding 
more than one. Having attribution at the bottom is minimal and announces the topic 
If we want to link to the project, you could do this in the about gist?

![screenshot_2013-03-11Screen Shot 2013-03-11 at 11 03 27 AM](https://f.cloud.github.com/assets/61150/244064/f478eea6-8a5c-11e2-81fe-1507989a0a61.png)