Added drawcalls example for buffergeometry

I've created an example of using ```drawcalls```on ```buffergeometry```to dynamically modify the number of points and lines to paint.
It's used both on a lines set and a pointcloud.

You can see here the working example:
http://kile.stravaganza.org/lab/js/examples/webgl_buffergeometry_drawcalls.html
Refactor your code a bit and try `controls = new THREE.OrbitControls( camera, renderer.domElement );` so the GUI does not compete for the mouse events.