Added model group support, you can now have multiple meshes in one export.
Removed OBJ and mesh replace export options.
Mesh replace didn't work, might get added again in the feature.
OBJ needs to be rewritten as well to support the multiple meshes, and Unity now has model export options in engine.
Version 1.8.0+ is now only supports Unity2018.3+.
Moved/changed replace OBJ to ReplaceMesh.
Optional model/texture/material export.
Added Material export option, set shader and shader properties to assign exported textures.
Added Prefab export option, exports mesh as an Unity .asset file and creates a prefab to link it to the mesh filter/renderer, added the option for auto assignment of the exported material (New default).
