Merge branch 'hotfix-4.5.1'
Update README.md

Updated links.
Add Xflow WebCL image processing unit test
Updated copyright
Removed deprecated physics implementation
Moved shader directory into gl directory
Add Xflow js platform tests
Add Xflow WebCL platform tests
Separate Xflow platform tests into fallback and targeted platform tests
Improve Xflow operator platform selection logic
Add an event listener in MatchTexture test
Fix false timeout problem in MatchTexture test
Improved some debug/info messages
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'
Update README.md
Merge branch 'release-4.6' into develop
Bugfixes with handling of visibilty.