Changed TriangleMesh::materials_ to be a std::vector<std::pair<std::string, Material>> so that the order of materials when loading a mesh is respected.
Using the unordered map caused issues when a Default Material and a texture were loaded and the texture would end up as the second material in the iterator.
Now TriangleMesh::triangle_material_ids_ will indicate what material index should be used.
A warning is given when passing a TriangleMesh to the visualizer and more than one material index is found, and the minimum value found in TriangleMesh::triangle_material_ids_ is used.
If no triangle_material_ids_ exist then the first material in the order they are loaded will be used.

…iangle mesh model

…is required

…y its materials into a TriangleMeshModel

…cluding textures

…ngs. Removed dead code.

… Exporter

…Mesh as well as for exporting a TriangleMeshModel to GLTF

…than one material was in use.

…4 byte boundaries

…was provided

…g for remapped vertices correctly.