Updated copyright
Removed deprecated physics implementation
Moved shader directory into gl directory
Fixed a bug that would cause exceptions when setting the shader of a group with a child Light element

- RenderLight doesn't implement the setShader function, and rather than add it (which would lead to confusion
with LightShaders on Light nodes and normal Shaders on group nodes) I added a check instead
Fixed an improper use of Array.splice in RenderLight. Lights should be correctly removed from the scene now
Update README.md
Merge branch 'release-4.6' into develop