Add system indicators back to data page

Since `formatted_value` got removed from the API indicators response, system-level indicators weren't displaying on the data page.  This adds back the (unformatted) data value for system indicators, instead of displaying "No Data Available."  Also puts into translation files some untranslated strings.
It should still be returned though by the serializer, so something is probably wrong there - https://github.com/WorldBank-Transport/open-transit-indicators/blob/develop/python/django/transit_indicators/serializers.py#L90