NiSwitchNode enhancements

[hexabits]

[description WIP]

NiSwitchNodes toggle visibility between two different NiNodes. It would be nice to provide some kind of UI for NiSwitchNodes to show the two states, one at a time. Currently both nodes are rendered all the time.

Other more general enhancements may come first, like storing visibility per mesh/node, and some kind of UI to toggle the visibility of any mesh/node. Regardless, it may be best to have a more specific UI for NiSwitchNodes, and maybe the secondary (i.e. non-default) state should be toggled off when the NIF is first opened.

[neomonkeus]

Just thinking state wise, would it be useful to have a third option where you enable both? Not sure if it's a valid use case, i.e checking for mesh overlap or if this is more modelling application-land. If its convenient to swap between the two would be enough.