[core] Rename item getter/setter

getDatas -> getItems
setDatas -> setItems

Note: Bridge->setDatas actually sets data, where Bridge->getItems
only returns items (this is why Bridge->setDatas was not changed)

formats/JsonFormat.php

@@ -7,7 +7,7 @@ class JsonFormat extends FormatAbstract{
 
     public function stringify(){
         // FIXME : sometime content can be null, transform to empty string
-        $datas = $this->getDatas();
+        $datas = $this->getItems();
 
         return json_encode($datas, JSON_PRETTY_PRINT);
     }