Click to show source code for feature demo

This implements @cjh1's idea about displaying source code for the generated features.

http://opengeoscience.github.io/geojs/examples/features.html
Something like that would be nice in the base class.  To what extent would it be possible to bind handlers to this kind of selection in vgl?  Could we have events like `mouseover`, `click`, etc. on gl features?  This is how I am using this in the demo app.