WebGL filters - first version!

Still a proof of concept and lot's of work ahead, but ColorMatrixFilter
is working!!
ColorMatrixFilter extensions
Some refactoring of filters.
Multiple render pass support for filters.
Minor refactoring and optimizations
Moved mask and shadow render code.
Changed RenderState.reset optional arguments
WebGL blur/glow/dropShadow filter
Minor code beautification

Probably not as fast as before, but much more beautiful.
Fixed canvas filter renderer
Simplified blur shaders
Added simple RenderFrameBuffer pool
Minor renaming
Some WebGL filter optimizations
WebGL filter fixes
WebGL filter fixes

Same as last one, but much smarter :)
Preparation for RenderTextureQuad filters
Make WebGL state changing methods public
Make renderFilter public to allow overrides
Fixed issue with odd width/height hi-dpi images