Import a landscape referencing non existing external functional flow into group

[julienthai]

Error occurs when importing a landscape which refers non existing external functional flow into group. (ADD channels refers flow of ADD lending not yet imported). As discussed a potential solution is to allow the import with warning saying that the target flow is not yet imported. We should create the group but not the link to the non existing functional flow. ID for such flow should be put in comment

A report may be useful in order to list such groups