CCEffectRefraction and other small CCEffect changes

- Adds first pass at CCEffectRefraction
- Adds refraction test to CCEffectsTest
- Adds node to texture transform to CCSprite in support of CCEffectRefraction
- Fixes node to world transform for CCRenderTextureSprite in support of CCEffectRefraction
- Makes CCEffectStack immutable by removing addEffect / removeEffect interface
- Misc API cleanup for other effects