[FIX] web_tour,web_editor: allow running tour in every context

Previous implementation allowed to run tour as a non-superuser but
this was only working in the backend where the static file tip.xml
is always loaded. In the frontend or in other non-backend context,
this file has to be loaded just before trying to launch the tour as
a non superuser (indeed, previous implementation loaded the file in
the frontend only if the user is a superuser).