How to handle radio group for NSButton

Issue #579

Use same action, or we can roll our own implementation

An NSButton configured as a radio button (with the -buttonType set to NSRadioButton), will now operate in a radio button group for applications linked on 10.8 and later. To have the button work in a radio group, use the same -action for each NSButton instance, and have the same superview for each button. When these conditions are met, checking one button (by changing the -state to 1), will uncheck all other buttons (by setting their -state to 0).

import Omnia

@IBAction func onModeButtonTouch(_ sender: NSRadioButton) {
    for button in [mode1Button, mode2Button] {
        button?.isOn = button === sender
    }
}