Added missing file.

plugin.xml

@@ -74,6 +74,7 @@
         <source-file src="src/android/Receiver.java"          target-dir="src/de/appplant/cordova/plugin/localnotification" />
         <source-file src="src/android/Options.java"           target-dir="src/de/appplant/cordova/plugin/localnotification" />
         <source-file src="src/android/Restore.java"           target-dir="src/de/appplant/cordova/plugin/localnotification" />
+        <source-file src="src/android/Helper.java"            target-dir="src/de/appplant/cordova/plugin/localnotification" />
     </platform>
 
     <!-- wp8 -->