Only load right hand popular component if article is > 500 words

This prevents a layout cluster fuck.

### before
![screenshot from 2014-02-07 17 35 18](https://f.cloud.github.com/assets/80089/2112446/cf40dd42-901e-11e3-8433-28679cf2f90e.png)

### after
![screenshot from 2014-02-07 17 37 22](https://f.cloud.github.com/assets/80089/2112447/d593245c-901e-11e3-973a-c407d18ec345.png)

/cc @NathanielBennett @cantlin