some refactorings

Author: vearutop

src/Structure/ClassStructure.php

@@ -42,4 +42,11 @@ public static function export($data)
     {
         return static::makeSchema()->export($data);
     }
+
+    public static function getAdditionalProperties(Schema $ownerSchema)
+    {
+        return null;
+    }
+
+
 }

src/Structure/ClassStructureContract.php

@@ -12,4 +12,5 @@ interface ClassStructureContract
      * @param Schema $ownerSchema
      */
     public static function setUpProperties($properties, Schema $ownerSchema);
+    public static function getAdditionalProperties(Schema $ownerSchema);
 }