Import, data sources, file recursion

see: https://groupes.renater.fr/wiki/txm-info/public/data_sources#recursion

(from redmine: issue id 2833, created on 2020/06/03 by Matthieu Decorde)

• Relations:
  • relates #2832 (closed)
  • parent #1485

added import type::feature + 1 deleted label

changed milestone to %TXM 0.X.X

mentioned in issue #3379