Add new platform admin page

Added a new platform admin page, at '/plaform-admin-new' which shows
different data. This no longer offers the option to filter by test-key,
only by date, and also gives a more detailed break-down of the
notifications and failures sent with a normal / research key.

The existing platform admin stats page ('/platform-admin') has not been
deleted yet so that both pages can be compared.

app/navigation.py

@@ -79,6 +79,7 @@ class HeaderNavigation(Navigation):
             'live_services',
             'organisations',
             'platform_admin',
+            'platform_admin_new',
             'suspend_service',
             'trial_services',
             'update_email_branding',
@@ -421,6 +422,7 @@ class MainNavigation(Navigation):
         'organisation_settings',
         'organisations',
         'platform_admin',
+        'platform_admin_new',
         'platform_admin_list_complaints',
         'pricing',
         'privacy',
@@ -590,6 +592,7 @@ class OrgNavigation(Navigation):
         'old_using_notify',
         'organisations',
         'platform_admin',
+        'platform_admin_new',
         'platform_admin_list_complaints',
         'pricing',
         'privacy',