Use tags for organisation

Current case is that there will only be one organisation associated with a document, so primary_tag just returns the first. If this changes we'll need a way to mark an org as primary.

- Update presenter with tags/organisations
- Update tests
- Update view

Trello: https://trello.com/c/y41PIOlq/153-aaib-finder-viewing-reports-on-gov-uk-3
This should be `@document.format_name`, rather than an organisation name.