This function loads up information for modifying an existing group.

• Called by ?action=membergroups;sa=edit;group=x in 1.1 and ?action=admin;area=membergroups;sa=edit;group=x in 2.0
• Requires the manage_membergroups permission.
• Uses the edit_group sub template of ManageMembergroups.
• Also handles the delete button of the edit form.
• Redirects to ?action=membergroups in 1.1 and ?action=admin;area=membergroups in 2.0.
• Located in ManageMembers.php in 1.0.x