Get organisation metadata from tags

The Content API returns all tags for an artefact as part of the
response. Where possible we want to use those existing taggings rather
than attaching custom metadata in the details hash.
Remove duplicate line in JSON
Update static manuals to have organisation tags
Whitespace
Remove topics from manuals

Linking manuals to topics isn't work we're planning to do in the near
future.
Use web_url instead of path in links_to_sentence

The Content API returns tags with `web_url` properties, so if we use
this we don't need to wrap the organisation tags in presenters (nor will
we need to wrap future tags in presenters, such as browse sections and
specialist sectors).

Also update the method signature for `links_to_sentence` to not set a
(misleading) default value for its argument.
Merge pull request #42 from alphagov/make-organisation-metadata-work

Make organisation metadata work https://trello.com/c/3aCHludy/115-display-organisation-metadata-2