Earlier there was only a realm level setting for configuring
who can edit user groups. A new group level setting is also added
for configuring who can manage that particular group.
Now, a user group can be edited by a user if it is allowed from
realm level setting or group level setting.
This commit make changes to also use group level setting
in determining whether a group can be edited by user or not.
Also, updated tests to use api_post and api_delete helpers instead
of using client_post and client_delete helpers with different users
being logged in.