Show a tour when users first create a service

This commit adds a 3 screen tour, similar to those used on GOV.UK Verify
and Passports.

We guerilla tested this on Friday, and it really helped users to build a
mental model of how Notify works, so that when they’re playing around
with it they have a greater sense of what they’re aiming to do. This
makes concepts like templates and placeholders click more quickly.

https://www.pivotaltracker.com/story/show/116710119

tests/app/main/views/test_add_service.py

@@ -26,7 +26,7 @@ def test_should_add_service_and_redirect_to_next_page(app_,
                 url_for('main.add_service'),
                 data={'name': 'testing the post'})
             assert response.status_code == 302
-            assert response.location == url_for('main.service_dashboard', service_id=101, _external=True)
+            assert response.location == url_for('main.tour', service_id=101, page=1, _external=True)
             assert mock_get_services.called
             mock_create_service.asset_called_once_with(service_name='testing the post',
                                                        active=False,