Add support for UV coordinates in Raysect

[mattngc]

A number of use cases have now emerged which would benefit from the feature of UV coordinates, basically coordinates on primitive surfaces (https://en.wikipedia.org/wiki/UV_mapping). Primary use cases could include:

• Getting the surface coordinate of a ray intersection with a primitive (#323).
• Applying surface varying material properties (i.e. textures, coatings, etc).

Overall, this is quite a massive feature and should be done in phases.

1. Define an interface for UV coordinates at the primitive and material level.
2. Contribute UV mapping classes on a primitive by primitive basis. Allowing gradual build up towards the feature.
3. Add UV coordinates and primitive identification to the Intersection() object.

Completing this issue would enable new classes of physically realistic materials as well as open up many useful utilities.