fix for DOCS-2709: document preview loading slow if via direct link

The viewer prebuilds a boiler plate for all files in a folder, which includes the attachment of eventlistener.

I moved the attachment of eventlistener to the "show phase" of a view, instead of adding them initially. So they are only attached on demand now (less overhead)

With many files (5000+) in a folder (which some customers seems to use), attaching 5000+ eventlistner at once it in the render phase causes a slow down especially with dev tools open.