- Add new methods SetDefaultParameterInt and SetDefaultParameterFloat
       useful for setting default values in the method DoCreateParameters()
     - Add button Reset to each NumericalParameter, and connect this button
       to a slot Reset() setting the value to the default one if any, making
       the state HasUserValue and HasAutomaticValue to false

ENH: if a mandatory parameter belongs to a ParameterGroup (which is non mandatory) and the group is deactivated, it must not be considered as missing