Add service-specific versions of agreement page

Our usability testing found that jumping out of the service when going
to download the agreement made it difficult for people to find their way
back to the ‘Request to go live’ page.

This commit adds a duplicate, service-specific versions of these pages
which have the same content but:
- keep the service navigation
- have a link back to the ‘Request to go live’ page

app/navigation.py

@@ -234,6 +234,7 @@ class HeaderNavigation(Navigation):
         'service_add_email_reply_to',
         'service_add_letter_contact',
         'service_add_sms_sender',
+        'service_agreement',
         'service_confirm_delete_email_reply_to',
         'service_confirm_delete_sms_sender',
         'service_dashboard',
@@ -365,6 +366,7 @@ class MainNavigation(Navigation):
             'service_add_email_reply_to',
             'service_add_letter_contact',
             'service_add_sms_sender',
+            'service_agreement',
             'service_confirm_delete_email_reply_to',
             'service_confirm_delete_sms_sender',
             'service_edit_email_reply_to',
@@ -735,6 +737,7 @@ class CaseworkNavigation(Navigation):
         'service_add_email_reply_to',
         'service_add_letter_contact',
         'service_add_sms_sender',
+        'service_agreement',
         'service_confirm_delete_email_reply_to',
         'service_confirm_delete_sms_sender',
         'service_dashboard',
@@ -991,6 +994,7 @@ class OrgNavigation(Navigation):
         'service_add_email_reply_to',
         'service_add_letter_contact',
         'service_add_sms_sender',
+        'service_agreement',
         'service_confirm_delete_email_reply_to',
         'service_confirm_delete_sms_sender',
         'service_dashboard',