Add page to show all uploaded letters

Because we won’t be showing uploaded letters individually on the uploads
page any more we need a way of listing them. This should be by printing
day, to match how we’re grouping them on the uploads page.

This code reuses the notifications.html template, but flips the
precedence of the filename and recipient because I reckon when you’re
looking at uploads you’re thinking filename-first.

app/navigation.py

@@ -331,6 +331,7 @@ class HeaderNavigation(Navigation):
         'delete_contact_list',
         'upload_letter',
         'uploaded_letter_preview',
+        'uploaded_letters',
         'uploads',
         'usage',
         'view_job',
@@ -407,6 +408,7 @@ class MainNavigation(Navigation):
             'delete_contact_list',
             'upload_letter',
             'uploaded_letter_preview',
+            'uploaded_letters',
             'uploads',
             'view_job',
             'view_jobs',
@@ -696,6 +698,7 @@ class CaseworkNavigation(Navigation):
             'delete_contact_list',
             'upload_letter',
             'uploaded_letter_preview',
+            'uploaded_letters',
             'uploads',
         },
     }
@@ -1248,6 +1251,7 @@ class OrgNavigation(Navigation):
         'delete_contact_list',
         'upload_letter',
         'uploaded_letter_preview',
+        'uploaded_letters',
         'uploads',
         'usage',
         'usage_for_all_services',