Missing option: "edit OWN groups hierachy"

Issue Summary

Hi!

I am really missing access rule "edit OWN groups hierachy".
The current state is that when I'll give access "edit groups hierachy" to some role, then users of this role can edit subgroups on ALL groups - groups where they are not admins/members too.

So now if I give that access role to registered users, they can edit subgroups of their groups BUT they can edit subgroups of EVERY groups ant it can be really confused for them.

This is why I suggest to add new access rule "edit OWN groups hierachy" or "edit groups hierachy only on groups where I am admin"

Please tell me what you think about it.
Thanks for your work on this module
Igorik
http://www.somvprahe.sk