SceneShapeUI: Rewrote DAG Menu creation to use `IECoreMaya.Menu`
SceneShapeUI: Rewrote DAG Menu creation to use `IECoreMaya.Menu`

Breaking Change
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Callbacks registered via `addDagMenuCallback` should now have the signature `callback( menuDefinition, sceneShape )` instead of `callback( menu, sceneShape )` and have to use the menu definition to add new entries / modify exisiting ones.

appleseedhq/cortex,appleseedhq/cortex,appleseedhq/cortex