* Replace method CheckMetaElements by CheckManadatoryElements

* Replace method CheckMetaElements by CheckManadatoryElements
  To deal with the pb of UID's, and with Type 1 an Type 2 Entries
  (probably some stuff still missing)
 * We shall have to decide the way we proceed to allow user 'freeze' Serie UID
      between a given call and the next one (to add images to a Serie he just
		created)
 * We shall have to decide the way we proceed to allow user 'freeze' Study UID
      between a given call and the next one, or to reuse an already existing
		Study UID (i he wants to add his own Series to an already existing Study)