Fix duplicated bulkCreation id in csv import Web UI extension

https://github.com/nuxeo/nuxeo-csv/blob/master/nuxeo-csv-web-ui/src/main/resources/web/nuxeo.war/ui/nuxeo-csv/nuxeo-csv.html#L28 has

  <nuxeo-document-import-csv id="bulkCreation"

but this bulkCreation is used by https://github.com/nuxeo/nuxeo-web-ui/blob/master/elements/nuxeo-document-create-popup/nuxeo-document-create-popup.html#L91

This is not a big issue but it might break some logics/scripts relying on id selector.