Add cronjob analytics to instructor dashbaord

Add a graph and dropdown for analytics from the analytics cronjob.
Refactor analytics section to have widgets (things with a template which can instantiate from a div with data attributes), like the list widget in the membership section.

![gd](https://f.cloud.github.com/assets/705646/910758/e541f54e-fddf-11e2-9fec-b79ff27c8053.png)

Also, space out the student admin section a little.

Reviewers:
@singingwolfboy 
@rocha