Allow for More Room with Ping Perms

In the role settings, please allow for admins to manage which roles another role can ping. Our server setup works on solid RBAC and I trust some members with the ability to ping some roles (VC ping or News alerts) and not others (@everyone and @[member access]).

I know it could possibly complicate role settings UI, but I see a great deal of potential for this. Especially given my use case, I can imagine a lot of people benefitting from this kind of setting.