Release 26.0.0

www.agileplannerapp.com/boards/173808/cards/8707

Removes `Expectation` model and introduces `need_to_know` `String` field on
Transaction, LocalTransaction and Place editions to store the expectations
as a govspeak field.

Releases: https://github.com/alphagov/govuk_content_models/pull/257
Merge pull request #258 from alphagov/add-need-to-know-fields

Release 26.0.0