User groups

[mellowagain]

Groups (as called similiary on GitLab and called organisations on GitHub) are a namespace under which repositories and all their data can be stored without belonging to a specific person.

Currently this issue is low priority as for the start organisations can just create an additional user on GitArena under which they can host their projects. We will allow individual accounts to be turned into groups once they are finally implemented. (Similiar to how Sourcehut is currently [December 2021] doing it)