Supported nested groups management in the Confluence UI

Support nested groups management via the Confluence UI

Example:
Group: PARENTGROUP contains user: A, B, and C. However, we want to add all of the users from another group, ANOTHERGROUP to the PARENTGROUP. Therefore, if ANOTHERGROUP had users: D, E, F, and G, making ANOTHERGROUP a subgroup of PARENTGROUP would give PARENTGROUP users A, B, C, D, E, F, and G. Though logically Confluence could display the idea of a "subgroup", the core functionality of this subgroup feature would be the ability to merge group members from different groups when needed. Likewise, whenever the time came to remove the subgroup, the "remove selected subgroup" feature would take all members associated with that subgroup out of the parent group. In context with the example above, PARENTGROUP, after removing ANOTHERGROUP from being its subgroup would only contain users A, B, and C again.