WebGL filters

This is the first version with full support for WebGL filters. WebGL filters are many orders of magnitude faster than the previous filter implementations in JavaScript. Those JavaScript based filters are still available and can are used with the Canvas2D renderer if a cache is applied to the DisplayObject (like before). 

WebGL filters are rendered in real time and can be combined in any way.
New filters will be added in a few days: DisplacementMapFilter and ConvolutionFilter.
Some performance improvements simple DisplayObjects (like Bitmap) will follow too.