Current implementation of the Color Blend State worked for framebuffers
with a single attachment. This PR adds support for Color Blend State for
multiple attachments. It is assumed that the Blend State is the same for
all attachments.
NOTE: Integer based attachments aren't yet supported. In OpenGL it is
assumed that Integer based attachments aren't blended. It is currently
to early to tell if this is also the case for Vulkan. If this assumption
is incorrect we should use multi blend state.
Jeroen Bakker