Added PagedLOD feature, with a new quadtree example. Also added computation of the projected bounding sphere size in pixels to the Lod class.
Using Vec3.create() instead of manually create vectors. Changes to the class variable names to use osg notation. Using osg.Notify instead of console.log
Fixed range calculation for PagedLOD when using pixel_size_on_screen
Merge pull request #58 from jtorresfabra/plod_impl

Added PagedLOD feature, with a new quadtree example.