Add a tour for users new to broadcast services

This is an initial, prototype-quality attempt at introducing some kind
of tour for users new to broadcasting. A lot of the users we’re speaking
to don’t have a good concept of what broadcasting means, which is
causing usability problems down the line.

We did a similar thing in the early days of Notify to explain the
concept of message templates and personalisation.

tests/app/main/views/test_broadcast.py

@@ -94,6 +94,7 @@ def test_empty_broadcast_dashboard(
     client_request,
     service_one,
     mock_get_no_broadcast_messages,
+    mock_get_service_templates_when_no_templates_exist,
 ):
     service_one['permissions'] += ['broadcast']
     page = client_request.get(
@@ -114,6 +115,7 @@ def test_broadcast_dashboard(
     client_request,
     service_one,
     mock_get_broadcast_messages,
+    mock_get_service_templates,
 ):
     service_one['permissions'] += ['broadcast']
     page = client_request.get(

tests/app/main/views/test_register.py

@@ -319,6 +319,7 @@ def test_register_from_email_auth_invite(
     mock_accept_invite,
     mock_create_event,
     mock_add_user_to_service,
+    mock_get_service,
     invite_email_address,
 ):
     sample_invite['auth_type'] = 'email_auth'
@@ -372,6 +373,7 @@ def test_can_register_email_auth_without_phone_number(
     mock_accept_invite,
     mock_create_event,
     mock_add_user_to_service,
+    mock_get_service,
 ):
     sample_invite['auth_type'] = 'email_auth'
     with client.session_transaction() as session:

tests/app/main/views/test_verify.py

@@ -178,6 +178,7 @@ def test_activate_user_redirects_to_service_dashboard_if_user_already_belongs_to
     sample_invite,
     api_user_active,
     mock_login,
+    mock_get_service,
 ):
     mocker.patch('app.user_api_client.add_user_to_service', side_effect=HTTPError(
         response=Mock(