Fix #1448 (Public shelfs are accessible even if not logged in)

cps/shelf.py

@@ -308,6 +308,7 @@ def delete_shelf(shelf_id):
 
 @shelf.route("/shelf/<int:shelf_id>", defaults={'shelf_type': 1})
 @shelf.route("/shelf/<int:shelf_id>/<int:shelf_type>")
+@login_required
 def show_shelf(shelf_type, shelf_id):
     shelf = ub.session.query(ub.Shelf).filter(ub.Shelf.id == shelf_id).first()