Use group types for group relation config
Our parent/child group system is not very usefule currently, because its semantics are unclear and are used in various ways.
We could use group types to define what the relation means, and to bind logic to it. Example optoins could be:
- Inherit permissions from parent to children
- Inherit permissions from children to parent
- Keep parent group in sync with all child groups
- Keep all child groups in sync with parent group
Apps could also use this if we let them define their own (app-managed) group types with pre-defined configuration. This could be used by Alsijil to define different kinds of course groups for attendance, etc.