Expansion/Preset selection callback

[d.healey]

@Christoph-Hart I'd like a callback to be triggered when the preset browser row selection changes. I'd like to be able to retrieve the selected column and row, if it's the expansion column I'd like it to return the expansion object.

I tried to implement this myself but quickly got lost with how to trigger my custom function correctly from the selectionChanged function. Could you implement this or give me some guidance on how to do it myself? Thanks!