Improved Composer all over

- added settings parameter to Composer constructor, to specify if it should use alpha
- moved MeshBasicMaterial to a default material in the prototype
- added .input and .output to address flip-flop buffers from outside composer
- changed all instanceof for Pass.isLoaded()
- removed unnecessary Shader creation for every Pass
- fixed MultiPassBloomPass to correctly used downsampled buffers
- added parallel processing of composers in MultiPassBloomPass
- added CGAPass
added teapot model for testing
added JSONLoader to load teapot
added more passes to test