[CWEP002] properly handle serialization of computed relations
We now:
* have CWComputedRelation in the bootstrap schema to store computed relations
* properly serialize/deserialize it
* test first if the database has been migrated and contains the related table
Related to #3546717
[jcr: adjust unittest_querier to pass with the added entity type]
Upstream Author:
%(author)s <%(author-email)s>
Copyright:
Copyright (c) %(year)s %(author)s.
%(author-web-site)s -- mailto:%(author-email)s