Group inheritance should not require membership on the parent group

[gdorsi]

Currently, extending a group requires the account to have access to the parent group, specifically with writer permissions.

We want to remove these requirements as they are more related to implementation constraints rather than real limits on the Group modeling.

This shoud help on setting more restirctive permissions on e.g. Workers, because this way it would be able to give permissions on a dynamic Group of members without being part of it.