Awesome print gem

For awesome printing.
Update GDS API adapters
Expose format specific fields via the class

So they can be used to construct the stricter
Rummager queries that require each return field to
be explicitly requested.
Switch search backend to Rummager
Rename `slug` -> `link`

Rummager returns `link` anyway, and it's about as descriptive as `slug`,
so let's just use that and cut out a layer of data structure massaging.
Make summary work for Drug Safety Update

Always request `description` from Rummager and let the format specific
presenters decide whether to use it.
Remove low value model specs

Specs removed here were just duplicated examples that were a pain to maintain
and offered little value.

There sholud be a test or shared example group for the super class to verify
the shared behaviour.
Remove `published_at` from MHRA formats

This information is not yet provided to Rummager
Simplecov for test coverage
Bugfix link presentation and rename to path
Remove unused `#to_partial_path` methods
Merge pull request #72 from alphagov/rummager-integration2

Use Rummager as search backend