Include `user` in *all* Slot Property Documentation

https://doc.nuxeo.com/n/m0B#document_views_items

Just above this part of the page there is a “Tip” that says “The model of every slot exposed by Web UI as the current user available under the user property.“; “as” should be “has”. Fixed

However I also think it’s a bit too obtuse to hide this information here. The presence of the `user` property should be part of each property list. For example `BLOB_ACTIONS` has `user` included in its property list explicitly. We should just do this for every slot and remove the “Tip” IMO as there’s no guarantee the reader will even notice the tip when looking for a specific slot.