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

app/main/__init__.py

@@ -23,5 +23,6 @@ from app.main.views import (
     api_keys,
     manage_users,
     invites,
-    all_services
+    all_services,
+    tour
 )

app/main/views/add_service.py

@@ -44,7 +44,7 @@ def add_service():
                                                        user_id=session['user_id'],
                                                        email_from=email_from)
 
-        return redirect(url_for('main.service_dashboard', service_id=service_id))
+        return redirect(url_for('main.tour', service_id=service_id, page=1))
     else:
         return render_template(
             'views/add-service.html',

app/main/views/tour.py

@@ -0,0 +1,15 @@
+from flask import render_template
+from flask_login import login_required
+
+from app.main import main
+
+
+@main.route("/services/<service_id>/tour/<int:page>")
+@login_required
+def tour(service_id, page):
+    return render_template(
+        'views/tour/{}.html'.format(page),
+        service_id=service_id,  # TODO: fix when Nick’s PR is merged
+        current_page=page,
+        next_page=(page + 1)
+    )