#896 Subgroups belonging to multiple groups

[mpatasiu]

Perhaps it would be possible to have subgroups belonging to more than one group? For example, group "Biochemistry" would be a subgroup of both "Biology" and "Chemistry". Currently the user has to make an arbitrary choice in such case.

One (perhaps relatively simple) way to do it might be having a type of group that is just a link to a different group.

Thank you in advance.