Generalise person relationships

Currently, we have only one kind of relationships between persons: guardians, which are hard-coded for school purposes.

We should turn this into a general relationship system, so we can dynamically add other kinds of relationships (e.g. emergency contacts).

Along the lines of #577 (closed) and #406, we should try to evaluate how to put this together with group roles, as with a generic person relationship, basically we get a "person role" of one person for another.

If it makes sense, we can also extend the "group type" concept to "person types", so that we effectively manage persons and groups using the same concepts.

added part::backend type::feature type::refactoring workflow::discussing labels

assigned to @hansegucker

unassigned @hansegucker

mentioned in issue #1226 (closed)

created branch 591-generalise-person-relationships to address this issue

mentioned in merge request !1746 (merged)

closed with merge request !1746 (merged)

mentioned in commit 480f14ea