TMDM-7626 : "Error while saving composite keys staging record"

Fix copy() issue for entity types (copy loosing key field declaration original order).
Adds unit test for issue.
(https://jira.talendforge.org/browse/TMDM-7626)
Merge branch 'maintenance/5.6' of https://github.com/Talend/tmdm-server-se
TMDM-3449 : beforeDeleting error message cannot be displayed in WebUI

  -- exception process handling beforeDeleting error message

  -- using alert messagebox & webUI should not proceed as if there is a error.