ENH: Improved the UI (and Specification) for EditFreeFormAttribute Op
The type of property being created/deleted is now explicitly modeled. Removing a property is now indicated by enabling the "remove" item. You can now how different property types with the same name.
Also cleaned up the UI so that Value is only displayed when specifying int, string, or double properties. Also removed "optional" flag for coordinate system properties and improved its use of space by turning off its item label (done by setting its label to " ")