[NavKit] Export texture hashes

[dbierek]

This PR has NavKit enhancements for the Editor API and server.

• Refactors the cumbersome tuples that were being passed through various functions into a class
• Gets the materials for each prim including diffuse, specular, and normal texture hashes
• Sends the prim hash -> materials hashes mappings (the primMatis array)
• Sends the material hash -> texture hashes mappings (the matis array)