© 2018 Author(s). This is an open access article distributed under the terms of the Creative Commons CC-BY License (http://creativecommons.org/licenses/by-nc/4.0/).

Creative Commons-lisensen er mer spesifikt Attribution 4.0 International (CC BY 4.0).
Except where otherwise noted, this item's license is described as © 2018 Author(s). This is an open access article distributed under the terms of the Creative Commons CC-BY License (http://creativecommons.org/licenses/by-nc/4.0/). Creative Commons-lisensen er mer spesifikt Attribution 4.0 International (CC BY 4.0).