SerializableArrayList now support post-deserialization

* Calling deserialize() over SerializableArrayList can be
  controlled by SerializableCollection.deserialize_proceed()
  for post deserialization using
  SerializableCollection.deserialize_children()

* SerializableCollection.deserialize_children() now uses
  internal GXml.Node to deserialize from

* Tests shows a improvement on document loading but a penalty
  on post deserialization of about 20% above in total time
  (loading+post-deserialization) Vs. (load+deserialization)