entities: allow user without person

Signed-off-by: Bas Westerbaan <bas@westerbaan.name>
Add <mongoid>@karpenoktem.nl

We add it for all entities, because if we would only add it for those
without name, we would break an address if it would get a name.

Signed-off-by: Bas Westerbaan <bas@westerbaan.name>
Also-known-as: 4e6fcc85e60edf3dc00001d4@kn.cx
entities: user:  Do not break when is_active is not set

Signed-off-by: Bas Westerbaan <bas@westerbaan.name>
entities: make primary_study more robust

Signed-off-by: Bas Westerbaan <bas@westerbaan.name>
Merge pull request #110 from khandhas-infra/externals

Externe gebruikers