Allow normalmaps to be loaded by themselves

[Major Cooke]

Is it possible to have the engine not require a specular map to load a normalmap? I feel it's arbitrary that one is needed in order to do so and it doesn't make much sense. Can't it assume something like an image that's pure black be loaded in its place in the event it's not added?

[Graf Zahl]

There still needs to be a specular texture to make the shader happy, but that could be provided b< the engine.

[Major Cooke]

Yes. A simple file like this will do perfectly, which the engine could default to if none is provided. Same with the other ones.

[Major Cooke]

I could try to make a PR for this as I'm curious about setting up a default, but is there anything special I need to consider for this?