Checkbox: setting checked now fires OnChange event
Checkbox: setting checked now fires OnChange event

Before the OnChange was not fired, but now it is. The only exception is while
the widget is in the UI Designer form.

wkitty42/fpGUI,wkitty42/fpGUI,wkitty42/fpGUI,wkitty42/fpGUI,wkitty42/fpGUI,wkitty42/fpGUI