Move serializers only used by gregui.

Queries iga for an external id matching ours. If a match is found, the
name of the owner is returend. Otherwise we return null. Uses the new
iga module to fetch the data.

Verify that the backend accepts unicode for text fields and that it
survives to the database and back again

If the user logs in through the frontpage we now check if they have
completed the registration process. If they have completed it halfway
before, we find their info through the GregUserProfile of the user and
redirect to the register page. If we dont find any profile connected to
the user they are treated as anonymous users as before.

Resolves: GREG-164

Resolves: GREG-173

Issue: greg-112

It has been decided that a sponsor at a unit should have access to all
roles at that unit. This includes all units accessible through
hierarchical access.

Resolves: GREG-150

- Combine the /invite and /invitelink endpoints into one
- Return error messages from the backend
- Handle errors in the frontend
- Lower number of queries ran when calling the userinfo endpoint

Used to "log" a user out in the manual invite flow

Serialization has been moved to serializer classes, sharing them when
sensible and Views have been converted to ViewSets to simplify code.

Separates the queryset and the serialization from each other.

The OU view deserves its own file, and the guest info is actually a
person view and should live with  the other person views.

The profile page of a guest now shows a verification button if the guest
has a passport or national identificaiton number that has not been
verified. Clicking the button shows a dialog, with a confirmation button
which triggers a PATCH request to the backend and reloads the page when
it returns.

Resolves: GREG-101