Add minimum version to RDMO XML exports

[jochenklar]

Description / Beschreibung

Right now, RDMO XML content files cannot be imported in instances, which have an older RDMO version than the file was exported from. Instead of relying on the version attribute, the export should have a required attribute, which denotes the minimal RDMO version this file can be imported in.

[MyPyDavid]

Will there be another issue about that an RDMO instance, currently, does not support importing from future versions?

rdmo/rdmo/core/xml.py

Line 50 in 1eadee5

if root_version > rdmo_version:

[jochenklar]

This is exactly what this issue is about. We would change this line to required_version > rdmo_version.