Allow Editor notes to have tags

www.agileplannerapp.com/boards/173808/cards/5154

Editor's notes were being validated as govspeak
causing safe html checks to fail. We've made an
exception in the SafeHTMLValidator to validate
only govspeak fields:

https://github.com/alphagov/govuk_content_models/pull/236
Consolidate publication table views

* Remove duplicated published edition partial
* Add a little extra logic to publication partial
Merge pull request #273 from alphagov/bump-content-models-for-safe-html-change

Allow Editor notes to have tags
Merge pull request #275 from alphagov/pub-table-partials

Consolidate publication table views
Form and display of important notes as actions.

Important note model has changed from a string on the Edition model to an
instance of Action, to allow including author and timestamp.
Controller and form to resolve important notes.
Migration to convert important_notes to actions.
Correct reference to note in index view.