* Move Documents used by several bt5 to erp5_core rather than add depends on erp5_core.
  Once migration of Products to ZODB Components will be finished, there will be moved to
  their appropriate bt5s as it would be complicated to reorganize bt5s too at this point:
  + DeliveryCell: used by InvoiceCell Document.
  + DeliveryLine: used by erp5_ui_test.
  + InventoryCell: used by erp5_archive.
  + InventoryLine: used by erp5_accounting.