[FormatInterface] Add missing public functions

This commit adds all missing functions to the interface
that are defined and implemented as public functions in
FormatAbstract.

lib/FormatInterface.php

@@ -1,6 +1,11 @@
 <?php
-interface FormatInterface{
+interface FormatInterface {
 	public function stringify();
 	public function display();
 	public function setItems(array $bridges);
+	public function getItems();
+	public function setExtraInfos(array $infos);
+	public function getExtraInfos();
+	public function setCharset($charset);
+	public function getCharset();
 }