Failing feature
HeadingValidator understands translation columns

Allows translatable columns to be specified. Translations are
optional, but if a "locale" column is present, any required fields
that have been marked as translatable must have a
corresponding tranlsation column of the form
"#{field_name}_translation". The "translation_url" is also required
if a "locale" column is present.
Update Row to recognise the translatable fields

At present, we are only interested in translating the title, body and
summary of news articles and speeches.
Expose translation attributes for NewsArticleRow
Import saves translations when present
Save a DocumentSource for imported translations

As well as saving the source url, we also note the locale. This is
so that the redirection urls we generate can point at the appropriate
translated version.
Make Speech imports translatable
Update DocumentMapper to be translation aware.

This makes two changes:

1. Exports now include a line for all the document sources for any
given document. This is required because detailed guides are
potentially imported from multiple sources.

2. The generated public urls map to the appropriate translation for
the document source. i.e. if the source document was a Welsh
translation, the public url points to the translated version.