Deletion of child ontologies

[eugenk]

We have no defined behaviour of the deletion of child ontologies.

Scenario:
When I upload a distributed ontology D with children C1, C2, ..., Cn
And I upload a new version of D1 with children C1, C2, ... C(i-1), C(i+1), ..., Cn
Then Ci should be inactive in the newer version, but active in an older version.

Currently, this makes our application fail (see #1593).