Added central management of shader binding.
Added in-node shader handling.
Changed scene draw API to pass the whole camera.

In the draw call the uniform locations are calculated from the shader
and not passed. You also need to pass the camera to get projection
matrix. This way you have all the information to prepare the shader and
can use arbitrary shaders in every node (hopefully).
Arbitrary shaders per object. Forward rendering too.
Solved depth and background problems.
Removed debug output.
Merge pull request #6 from TheSlothExperience/super-scenegraph

Super scenegraph