Received: 27 May 2019
Accepted: 11 September 2019
First Online: 28 October 2019
Ethics approval and consent to participate
: In accordance with French law, no ethical approval was needed.
: All authors have completed the Unified Competing Interest Form (available on request from the corresponding author) and declare: no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous 3 years; no other relationships or activities that could appear to have influenced the submitted work.