Modernize invertergui: MQTT write support, HA integration, UI updates

mk2driver/mockmk2.go

@@ -37,6 +37,22 @@ func (m *mock) Close() {
 
 }
 
+func (m *mock) WriteRAMVar(_ uint16, _ int16) error {
+	return nil
+}
+
+func (m *mock) WriteSetting(_ uint16, _ int16) error {
+	return nil
+}
+
+func (m *mock) SetPanelState(_ PanelSwitchState, _ *float64) error {
+	return nil
+}
+
+func (m *mock) SetStandby(_ bool) error {
+	return nil
+}
+
 func (m *mock) genMockValues() {
 	mult := 1.0
 	ledState := LedOff