add action to context menu to replace single set fit parameter with general fit parameter

src/gui_qt/fit/fit_parameter.py

@@ -78,6 +78,7 @@ class QFitParameterWidget(QtWidgets.QWidget, Ui_FormFit):
             widgt.state_changed.connect(self.make_global)
             widgt.value_requested.connect(self.look_for_value)
             widgt.value_changed.connect(self.change_global_parameter)
+            widgt.replace_single_value.connect(self.delete_single_parameter)
 
             self.global_parameter.append(widgt)
             self.scrollwidget.layout().addWidget(widgt)
@@ -148,6 +149,13 @@ class QFitParameterWidget(QtWidgets.QWidget, Ui_FormFit):
         if value is None:
             self.change_data(self.comboBox.currentIndex())
 
+    def delete_single_parameter(self):
+        idx = self.global_parameter.index(self.sender())
+        for i in range(self.comboBox.count()):
+            set_id = self.comboBox.itemData(i)
+            self.data_values[set_id][idx] = None
+        self.change_data(self.comboBox.currentIndex())
+
     def change_single_choice(self, _, value, sender=None):
         if sender is None:
             sender = self.sender()