Allow for GEGL nodes in texture creation

GEGL (Generic Graphics Library) came from Blender's cousins, the GIMP crew; specifically the team formerly known as Rhythm & Hues. As opposed to a simple linear (and destructive) filter system, it allows for nodular filters with potential multiple inputs and outputs, which may be connected to each other in an acyclic tree to produce a rendered layer—that's right, it's basically a node graph. And it's awesome .

I've been digging through the now-deprecated Texture Node Editor, and I feel like GEGL (which is entirely open) may be the way to go with upgrading it. It's extremely flexible; you can even write your own filters in a systems language. Once I've established a firmer grasp on the C/C++ side of Blender, I would even be willing to take this on myself, but it's already a perfect complement as an outside program and I would love to see it implemented.