Revamped versions usage page

 - improved SQL querying and simpler PHP processing
 - gradient doughnuts going from green to red (not entirely happy with color scheme, but easy to change)
 - weekly data points on line graphs for cleaner look

![wp-versions-usage](https://cloud.githubusercontent.com/assets/737584/5134267/2b3963ee-7115-11e4-8124-f01eb6aa3d84.png)