Add account detail list to management interface

[verigreppi]

Only allow SUPERADMIN role to view account details. For others return empty list.

[Anonyymi]

Thanks. This is only a read-only list though, do you want to improve it further to make it an editable form or shall I merge the PR as-is? It's a good start for an account management form.

[verigreppi]

Just merge it. We'll see if I get to implementing anything else.