[rmodels] Implement loading of mesh names from glTF/IQM/OBJ.

[arlez80]

This PR aims to implement loading of mesh names from glTF/IQM/OBJ and add a name member to the Model structure.

In glTF, node names are used as mesh names because Blender object names are written to the nodes.

For IQM, the mesh name is copied from the already loaded mesh name.

For OBJ, the mesh name is copied from objShapes[*].name.

[arlez80]

These image aren't part of this PR currently, would it be acceptable to add a sample for displaying mesh names to models_loading.c?
The reason I asked was that I was wondering if it would be better to put the sample in a separate file.

[raysan5]

@arlez80 I'm afraid it has already been proposed in the past and there is no intention for now to add those 32bytes of additional information to Mesh structure. Most users do not really need that information.