Tidy up GovUkDeliveryEndPoint#tags
Whitespace.
Add govukdelivery tags for roles & appointments on announcements
Tidy up test URLs for GovUKDelivery
Correct naming of email signups controller test.
Encapsulate filter options.

Prep work for simpler email signups.
Build a tool for describing feed URLs.
Pass feed URL straight through to govukdelivery.

This greatly simplifies the process of creating
email signups.

Rather than passing params to a form which sends
options a controller which then regenerates an
atom URL by parts, just pass the URL straight
through and ask the user only for a confirmation
of their subscription (with local government
opt-in).
Properly build and case document feed URL descriptions.
Properly describe non-document alerts

e.g. policies, people, roles
Refactor govuk delivery notification.

- Switched to Sidekiq
- GovUkDeliveryEndpoint:
  - extracted SubscriptionUrlGenerator
  - extracted EmailFormatter
  - renamed the remaining class to 'Worker' reflecting the fact that it is now
    only a simple wrapper for the async job.
- Removed the explicit autoloading configuration and instead rely
  upon Rails conventions.
Strip out the group from the options arrays because Rails.
[+DH] Refactor and test document filter options
Add feed validations to EmailSignup.