Exclude some users

1) to add an access permission so the superadmin, can delegate his/her vice-admin (this think is simple)
2) add option for to hidden some user and role in the list; this because for example if I am
the superadmin and assign the managment at my vice I not want to be in the list of user;
also I not want that my vice can manage all the roles of the site

3) also is useful to have an interface where the user can also to grouped;
so one can assign some roles at the user's group; and also is more clear to see
whic role have the users (this if one must to mange many users)