Allow altering visibility of button with routing

Allow altering the visibility of the Moderation Sidebar toolbar button by using routing.

I should be able to hook into the routing system and hide the button, by modifying the route requirements for the sidebar routes.

In addition, proxying a new entity operation through to the existing view operation would make detecting intent easier.

Motivation: I want to conditionally hide the button, and access to the sidebar routes, depending on the entity in context.