Add proper sidebar with comments, activity and versions (as in Files)

As Collectives operates on the same files it would be great to have the sidebar components of Files available. I don't know if it is technically possible to reuse the same components.

• Users want to discuss and comment changes before they apply changes to the document. → tab-comments
• Users want to see at a glance wich changes have been made to the page. → tab-activity
• Users want to revert changes. → tab-versions (already implemented in Collectives)
• (Talk and Share might not be necessary and maybe even confusing.)

Also the icon should be different from the left hand sidebar. NC typically uses an people/share indicator for right hand sidebars.

Thanks for considering and keep up the great work :-)