Untangle Publishing API from Panopticon registration

These are not the same things so we shouldn't use the same decorator class,
especially given Panopticon will eventually be retired.
PublishingApiPresenters::Organisation for consistency

Mirrors how we are doing adding editions to content store with Publishing API
Rename publishing API workers

Neither "register" nor "artefact" are terms that are appropriate for the new
publishing API. This renames the workers to better reflect what they are for.

Note that the old files are left in place with the constants set as temporary
aliases of the new classes. This is so that any jobs already queued against the
old worker classes can still be processed. This will need to be cleaned up in a
future commit.
Remove unnecessary queues

We don't set different priorities for these jobs so there is little point in
having a separate queue for them.
Add FIXME note for later cleanup
Fix GillSans font stack

* On IE neither GillSans nor Gill Sans were matching
* In Chrome on windows, Chrome has been known to pick “Gill Sans Ultra
Bold” instead

Applying fix from admin template:
https://github.com/alphagov/govuk_admin_template/pull/41
Merge pull request #1805 from alphagov/fix-gill-sans

Fix GillSans font stack
Merge pull request #1794 from alphagov/publishing-api-presentation

Clean up code that is publishing to Publishing API
Create new featured link table
Update models and unit tests for featured links

Remove top_tasks and featured_services_and_guidance and replace it with
just featured_links
Update references to top_tasks to featured_links
Add homepage types to organisations

Automatically set the type based on if there are any current featured
service and guidance link for a given organisation
More featured link and featured service guidance updates
Add new limits for featured links
Show correct number of featured links on org pages

Note: we are now only showing 7 featured service and guidance links
rather than 10. This is because in user research fewer links here have
proved to be more effective. This might be iterated in the future
though.
Update admin to show featured links
Add new feature link admin toggle
Update tests
Update permisions for managing org homepages
Add future migration to drop extra tables

These will no longer be used as the models have been deleted. Put in
pending_migration_cleanups so there are no errors while the code hasn't
restarted but the migrations have run.