Write a proper recreate_properties_on_undo function

[richeyrose]

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[richeyrose]

Blender's undo system undoes actions triggered by the load_post app handler when the appropriate undo step is reached.
Currently we check to see if our tile_defaults custom scene property is being unloaded and if it is we rerun create_properties_on_load. This is a bit hacky and should be made more robust. Really should be checking all properties and reloading only when necessary