add missing public interface for iOS client app id

lib/public/defaults.php

@@ -144,4 +144,12 @@ class Defaults {
 	public function getLongFooter() {
 		return $this->defaults->getLongFooter();
 	}
+
+	/**
+	 * Returns the AppId for the App Store for the iOS Client
+	 * @return string AppId
+	 */
+	public function getiTunesAppId() {
+		return $this->defaults->getiTunesAppId();
+	}
 }