Student contributions bugfix

Having an already minified script (protovis) in the js block was causing problems with django compressor, javascript didn't work properly (as you can see in the picture) and the dropdown menu items in the top menu bar didn't respond to clicks.

I moved the script to the extrahead block so it doesn't get compressed and now it works fine.

![mediathread_instructor_dashboard](https://f.cloud.github.com/assets/38059/856860/ec0434ee-f544-11e2-8f54-18f81e0a8fcf.png)