Fixed Blur postprocess effect XML. Fixed View spamming the log with attempts to get an empty quad shader after failing to get the proper shaders once.
Added the concept of persistent target in renderpath, which are not mixed in the rendertarget pool with other textures of same size & format. Used for the AutoExposure previous frame luminance.
Clear persistent float screenbuffers to ensure their contents aren't undefined. This fixes the AutoExposure effect on OpenGL. Added missing float textures to OpenGL Texture::GetDataType().