Add the ability to create user accounts with roles associated with a single mongodb

[gilbert-rehling]

Currently we have added the ability to create users with global roles: readAnyDatabase, readWriteAnyDatabase, userAdminAnyDatabse, dbAdminAnyDatabase - these are added to the 'admin' db scope

We want to be able to select deom the existing databases (depending on current permissions) and add a db/role scoped to the selected database.

This will enable the ability to create database centric users that can login the the application and only work on a desginated database