Fix docs in ServletInitializer
Switch to a matches-none filter for security.basic.enabled=false

There were some residual issues to do with the changes to the implementation
of security.basic.enabled=false. It was a good idea to have a filetr chain
triggered by the flag being off because it smooths the way for user-defined
filter chains to use the Boot AuthenticationManager (as a first step at least),
but it wasn't a goog idea to add any actual secuity features to that filter.
E.g. if it has HSTS then even an app like Sagan that has some secure endpoints
that it manages itself and the rest is unsecured has issues because it can't
accept connections over HTTP even on unsecure endpoints.

TODO: find a way for security.ssl_enabled=true to apply to only the user-
defined security filter (maybe not possible or worth the effort, since they
can inject a SecurityProperties if they need it?).

See gh-928