Add CustomPropertyUI

[skalarproduktraum]

This PR adds the CustomPropertyUI class in order to enable Commands to add their own UI items to the property inspector.

Custom UI based on a Command's inputs can be added e.g. as (taken from GameOfLife3D)

node.metadata["sciview-inspector"] = CustomPropertyUI(
                this,
                listOf(
                    "starvation",
                    "suffocation",
                    "birth",
                    "connectedness",
                    "playSpeed",
                    "play",
                    "pause"
                )
            )

The result then is the following:

[skalarproduktraum]

@RuoshanLan Do you have any additional requests for this one? I'd otherwise merge it 👍

[RuoshanLan]

@skalarproduktraum Currently not, please merge it, thanks! 👍