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).