As service provider I want to configure which kind of users can see the event counters

Opencast 2.x supports a facility named role-based visibility that allows service providers to adjust access to the admin ui in a both secure and fine-grained way.
Currently, it is not possible to configure what kind of users shall see the event counters.

The goal of this task is add make it possible to use role-based visibility to determine which kind of users can see the event counter.