Revisit Single page URL

[kdp-cloud]

Currently when the user selects something in the tree view of the single pages view, some ids are manually added to the URL that result in non-resolving URLs. This means that when a user navigates to an item in the single pages view and sends that URL to another user, it will not resolve to anything and always send users straight to the project instead of the item.

This has been done by design in the past but should be reverted.

A possible solution would be to get rid of the /single_pages endpoint altogether.