Deduplicate and add version validation of imports

[imsdu]

Motivation
With #5026 done, it is possible to improve schema import validation by checking the revision of the imports is consistent.

Acceptance criteria

1. A schema/ontology should appear only once in the fat schema even if it is imported several times
2. If schemas and ontologies are imported several times (via intermediate schemas), an error is returned to the user mentioning the candidates and where there were resolved from so that the user can take the appropriate action.