Make publishing api associated documents handle translations

[JonathanHallam]

This makes the publishing api associated documents service responsible for translations. Any associated document that has a translation will now be updated (published, withdrawn, discarded etc) along with the english language version.

Trello - https://trello.com/c/wTxdEIMS/1122-make-publishingapiassociateddocuments-handle-translations

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