Improve Monokai highlight style to match original

The current monokai style in highlightjs is not very true to the
original and lacks colors for certain syntactic items as mentioned in ticket #6855. This change's
goal is to bring the highlightjs monokai style in line with the original
design from http://www.monokai.nl/blog/2006/07/15/textmate-color-theme/

Here's the current monokai highlighting style
![monokai-old](https://cloud.githubusercontent.com/assets/9374/5034946/b8b87486-6b38-11e4-9dea-73034fd92e29.png)

After this change:
![monokai](https://cloud.githubusercontent.com/assets/9374/5034949/bf9cbf78-6b38-11e4-8b6b-65d48fdc0517.png)


Thanks!