Created by: micapam
As per #536 (closed), I've found that the default behaviour of showing links to all resources' index pages in the sidebar is rarely desirable.
I understand that it's possible to generate the sidebar and then put some logic in there - exclusions and the like. However, my experience from all use cases thus far (current project is the third time I'm using Administrate) tells me that this should be immediately available and obvious functionality. Thus this PR.