Implement Enable property values "inactive" and "off" for uicontrol Edit (bug #57128) * BaseControl.cc (updatePalette): Call setColor() with additional argument of "QPalette::Active" and again with "QPalette::Inactive" so that colors are set only for specific roles. When Qt widget disabled it should now go gray. * BaseControl.cc (init): Call 'setEnabled (! properties.enable_is ("off"))' so that "Inactive" value still causes Qt Widget to be enabled. * BaseControl.cc (update): Call 'setEnabled (! properties.enable_is ("off"))' so that "Inactive" value still causes Qt Widget to be enabled. * EditControl.cc (init): Check Octave "Enable" property and call Qt setReadOnly() if value is "Inactive", but otherwise call Qt setEnabled() with property value. * EditControl.cc (updateSingleLine, updateMultiLine): Check Octave "Enable" property and call Qt setReadOnly() if value is "Inactive", but otherwise call Qt setEnabled() with property value.