introduce interfaces for state/feedback topics

src/M433SwitchItem.ts

@@ -1,19 +1,27 @@
 import * as logger from './log'
 import { mqttHandler } from './MqttDispatcher'
-import { AItem } from './AItem'
+import { AItem, HasStateAndFeedbackTopic } from './AItem'
 import { SwitchExport, ExportType } from './Export'
 
 
-export class M433SwitchItem extends AItem {
+export class M433SwitchItem extends AItem implements HasStateAndFeedbackTopic {
     private offCode: string
     private onCode: string
     private oldState: string|undefined
     private state: string
     private actionTopic: string
     private stateFeedbackTopic: string
-    public stateTopic: string
+    private stateTopic: string
     private type: string
 
+    getStateTopic() : string {
+        return this.stateTopic
+    }
+
+    getStateFeedbackTopic() : string {
+        return this.stateFeedbackTopic
+    }
+
     constructor(floor: string, room: string, item: string, label: string, onCode: string, offCode: string, type: string = 'bulb') {
         super(floor, room, item, label)
         this.stateTopic = `${this.topicFirstPart}/state`