Activity charts

This branch starts working on implementing activity charts in the site to replace those that used to be on developer.joomla.org.  Still a long way to go, but this chart does render the data it's pulling correctly.

TODO list:
 - [ ] Test points aren't logged properly
 - [ ] Using the GitHub username versus the user's real name
 - [ ] Layout isn't optimized to the container width
 - [ ] Other charts from http://developer.joomla.org/tracker/volunteer-activity.html aren't ported (all of the component code is available at https://github.com/mbabker/bug-squad-stuff/tree/master/components/com_trackerstats)
 - [ ] Other optimizations or improvements based on feedback

@dextercowley if you have any suggestions or improvements you'd like to offer, I know I'd greatly appreciate the help.