Preference page's configuration selection is not directly displayed

When changing configuration selection to *Custom, RNC class A, B, C or D*, the user must *Apply* the configuration to have it being displayed in the two `TableViewer` of *Metric* & *Rules*.

This process isn't convenient for the user especially when setting when the preferences are already set on one of the RNC class and that the user choose "Custom" one as the Table stays not editable.