Adding sidekiq
Renaming ManualServiceRegistry to Organisational

We renamed this to create another ManualServiceRegistry which isn't
scoped by the User's Organisation.
Introduce a Publishing Workers Layer

This commit adds a workers registry which allows us to call a worker
from the controller which in turn can call the services and perform them
asynchronously.

Also allowing tests to run as normal when creating  background workers.
Remove slug pre-registration before publishing

* Wait until a document or manual is published
  before creating an artefact with Panopticon.
* Remove PanopticonMapping instead perform a GET
  request to check existence and either PUT or POST
  using slug.

NOTE:
* All panopticon communication is now via slug
* Panopticon PUT is only used for publishing a
  second version, withdrawal and re-publish.
Remove cruft from document repository spec
Cuke refactor - What even is a mapping?
Enable footnotes for specialist-publisher.

Footnotes were causing errors on publish because the sanitize gem (a
dependency of govspeak) was erroring with invalid HTML when attempting
to use colons in ids.

Upgrade sanitize, then upgrade govspeak, then upgrade
govuk_content_models (depends on govspeak), and now finally upgrade
specialist publishers versions of govspeak and govuk_content_models.

Add help text for footnotes taken from Whitehall.
GdsApiProxy supports not found
More stringent test for publishing second editions
Merge pull request #209 from alphagov/add-footnotes

Enable footnotes for specialist-publisher.
Merge pull request #200 from alphagov/introducing-workers

Introducing workers
Add Sidekiq and Redis config

Copies the approach used in other apps, eg Whitehall and Signon
Add note about Sidekiq to README
Merge pull request #211 from alphagov/add-sidekiq-config

Add sidekiq config
Merge pull request #210 from alphagov/change-panopticon-integration

Change panopticon integration
Validate manual section body with safe_html
Don't govspeak manual and manual section summaries

Summaries are for use as a short plain-text summary of the content in
places like search results pages. They shouldn't contain markdown, and
displaying them in the publishing tool processed with govspeak is
misleading for editors.
Validate manual section HTML before preview
Merge pull request #212 from alphagov/validate-safe-html-for-manuals

Validate safe html for manuals