Provide example showing how to wire up the signals with Blueprints

[Darryl Agostinelli]

It's unclear from samples how to wire up to a blueprint.

For example:

mybp = Blueprint('home', __name__, url_prefix='/')

@flask_saml.saml_authenticated.connect_via(app)
def on_saml_authenticated(sender, subject, attributes, auth):
  pass

This doesn't work.

I could also switch to flask.current_app, but then we get RuntimeError: Working outside of application context.