Make possible to filter allowed data sources. It is used for WebDAV curl, WEBSERVICE function, cell external references. Change-Id: Ifc82af31ff1123b5656a21e6a27624fb1616db39 Reviewed-on: https://gerrit.libreoffice.org/c/core/+/160196 Tested-by: Jenkins CollaboraOffice <jenkinscollaboraoffice@gmail.com> Tested-by: Caolán McNamara <caolan.mcnamara@collabora.com> Reviewed-by: Caolán McNamara <caolan.mcnamara@collabora.com> Reviewed-on: https://gerrit.libreoffice.org/c/core/+/161772 Tested-by: Jenkins Reviewed-by: Szymon Kłos <szymon.klos@collabora.com>
