Implement save method in collection reference repository

lib/Alchemy/Phrasea/Collection/Reference/CollectionReference.php

@@ -68,6 +68,18 @@ class CollectionReference
         return $this->baseId;
     }
 
+    /**
+     * @param int $baseId
+     */
+    public function setBaseId($baseId)
+    {
+        if ($this->baseId > 0) {
+            throw new \LogicException('Cannot change the baseId of an existing collection reference.');
+        }
+
+        $this->baseId = $baseId;
+    }
+
     /**
      * @return int
      */