Added RenderTarget class
Added clone() method for RenderTarget class
Added RenderTargetCube class

RenderTargetCube inherits from RenderTarget class with support for
dynamic cubemapping.
Added APass and RenderPass classes.

APass represents a rendering pass to be used by the EffectsComposer.
These will be used for multiple rendering pass effects.
TextureManager update. This commit is just to store my changes. It is far from ready for prime ime.