bake nodes update

"bake2d" and "bake3d" nodes are just a operation nodes, not root surface
nodes.
Since sometimes there's a need to have multiple bake operations in the
same shader.
surface-bake nodes are now named as "surface_bake2d" and
"surface_bake3d" correspondingly.
ShadingNormalCustom

The only difference from ShadingNormal is that it allows to set custom
normal as input. This is very useful in surface shader that also does
some displacement.
I wrote myself as an author, if you think it's not appropriate, write
"mesh" as it were.
invert nodes fix

removed duplicates
CC and math nodes

fixes and additions
displacement nodes
DRL's AOVs nodes