Adjust Texture Map Inputs To Utilize A More Dense Structure

[MartianDays]

At the moment, several textures are needed and utilized to build materials, but I believe this could be done more efficiently to cram more definitions into each file. This would allow for more integrations/definitions without greatly increasing texture memory load.

An example of how this could be implemented:
Texture 1:
RGB: Diffuse / Base Color
A: Greyscale Emissive

Texture 2:
RGB: Normal Map
A: Greyscale Parallax Occlusion Map

Texture 3:
R: Metallic
G: Roughness
B: Curvature Map
A: Transparency/Translucency

Could probably use cvars as well to enable/disable certain channels so the renderer doesn't need to test for them. It already does this to a degree. Things like translucency/transparency, parallax, and emissive we may want cvars for.