Add translations for rails date order

Not doing so caused crashes on applications which don't fall back to
English when a translation is missing.

We're adding them in a separate file so we can exclude it from crowdin
and so translators don't translate symbols as if they were words which
need translation.

config/locales/de-DE/rails_date_order.yml

@@ -0,0 +1,6 @@
+de:
+  date:
+    order:
+      - :year
+      - :month
+      - :day