Query when an axiom was added or removed

[bolerio]

This should be one of the benefits for the type of versioning module where all versioned items are structured DB entities. So we should be able to query in what revision was a given axiom added (or removed). Or more interesting queries, like which revisions affect a given entity by having axioms about that entity added or removed (and perhaps with the ability to specify property chains so we can query several degrees of separation).