Duplicate document names make documents inaccessible

The documents request URL is done by the name of the author and then the name of the document. This results in an internal server error when the author has multiple documents with the same name. This is very prevalent in AIV community solutions for example, because they have a standardized way of naming documents similarly to make it clearer.

This requires changing documents/urls.py, documents/views.py and the hooks in the frontend. Preferably it should use the ID of the documents instead of the name.

    path(
        "<str:username>/<str:slug>/",
        views.DocumentElementView.as_view(),
        name="element",
    ),