Render window no longer creates default renderer

Create renderer for each layer.
Fix setting of background colour
Fix caching of scene objects

Need to key of the scene MD5 and the part number.
Prevent skipping of layer zero
Add resetScene getter and setter

Need to be able to prevent the scene being reset for vtkWeb.
Prevent loop exit variable being calculated everytime
Add getter/setter for reset camera clipping range
Add hasActor(...) method to renderer

Add method to determine if a particular actor is already attached
to a renderer.
Refactor the fetching and parsing of VTK objects

Clean up implementation for parsing VTK objects.
Fix style issues
Add documentation for layer() and setLayer(...)
Merge pull request #47 from OpenGeoscience/vtkweb-updates

Vtkweb updates