Fixes to CCEffects

* Hid CCEFffects behind CC_ENABLE_EXPERIMENTAL_EFFECTS
* Fixed frame buffer leak that was caused by CCEffectNode
* CCEffects can now be added automatically drawn, thus we can add CCEffectNode to the scene
* Made sure CCEffectGlow and CCEffectBrightnessAndContrast correctly work with premultiplied alpha blend mode


TODO
* Figure out how to stack effects that are composed of multiple render passes
    * Break up certain effects, e.g CCEffectBrightnessAndContrast could be CCEffectBrightness and    CCEffectContrast
* Add CCEffects to CCSprites again
* Create a demo that shows off glow and motion blur.