feat(background-mode): added moveToBackground and moveToForeground (#1181)

feat(background-mode): add missing functions moveToBackground and moveToForeground as explained in #1180

Author: gujiman

src/plugins/backgroundmode.ts

@@ -123,6 +123,24 @@ export class BackgroundMode {
   })
   static on(event: string): Observable<any> { return; }
 
+  /**
+   * Android allows to programmatically move from foreground to background.
+   */
+  @Cordova({
+    platforms: ['Android'],
+    sync: true
+  })
+  static moveToBackground(): void {}
+
+  /**
+   * Android allows to programmatically move from background to foreground.
+   */
+  @Cordova({
+    platforms: ['Android'],
+    sync: true
+  })
+  static moveToForeground(): void {}
+
   /**
    * Override the back button on Android to go to background instead of closing the app.
    */