Separate AssetMaterial Library from Pathtracer

[ClemensLinnhoff]

The pathtracer is a good example to see OpenMaterial in action. But it is not only "just" an example. It contains classes and functions that could directly be used in other application. Especially those to read and store the geometries und material data structures.

I propose to separate these classes from the pathtracer example, so with an according documentation they can directly be included in other projects using OpenMaterial.

[LudwigFriedmann]

Extension of the pathtracer and corresponding re-factoring is currently in progress. This may be a follow-up activity. A stand-alone implementation of the proposed assetmaterial lib may even be synched with changes in the specification. Of course, this would have to be safe-guarded by corresponding tests.