Rejiggered the code-mirror code-blocks a bit

Tweaked the styling, the includes, and the scripting to work better and be slightly less hacky. 

Python includes now use <pre> for code blocks instead of ```. This means the html that Jekyll spits out is much cleaner and easier for codemirror to render. The code in the codeblocks is passed to codemirror is exactly as the user enters it, rather than stylized and then de-stylized.

Also code blocks are more visually consistent.