Add option to automatically apply a loose_material or mtlx material to the currently selected object if it doesn't have a defined use.

If a loose material or mtlx material with no defined use is detected, the addon should offer the user to apply it to the currently selected object, if applicable.

The same thing should happen with HDRIs, for which the logic is a lot easier because they are always "unreferenced" because there is only one per scene.