Remove unused checked assign

* Checked variable isn’t being used anywhere
Lock & hide display date fields if confirmed date

* When the date is confirmed, the display must be exact — users were
confused when they selected a date, the radio option changed but they
were still able to switch it back to one or two month precision
* Instead, switch to exact, lock the form field and hide the one and
two month options
Move release date fields into partial

* Stop repeating fields in new announcement and new date change forms
Upgrade Bootstrap from 2.0.3 to 2.3.2

* Delete old Bootstrap js and css assets
* Use Bootstrap SASS gem to load assets and to give access to SASS
variables and mixins
* Bootstrap changelog: https://github.com/twbs/bootstrap/releases
Allow organisation jobs link to be overridden

Organisation#job_url defaults to the civil service jobs search, but can
be overridden by setting the custom_jobs_url attribute.
Editors can add or remove detailed guide translations
Detailed Guides `Contents` heading is translatable
Regenerating locale files given new translation key
CSS change to horizontally align locale options
Edition already includes Translatable module
Mark detailed guide routing as localised
Remove condition that can't be reached

`best_locale_for_edition` redundantly checked `edition.non_english_edition?`. This is the first check in `document_url` and so would hit on that line, if correct, never inside `best_locale_for_edition`.
Add more translatable text to Detailed Guides show page

Add Welsh translations since the feature is primarily for Welsh readers.
Add remaining translation files
Commence translation controller refactoring

Move the `create` method to a module that extends ActiveSupport::Concern
Refactor: move `edit` method to Translation Concern
Refactor: move `update` method to Translation Concern
Refactor: move `translation_locale` method to Translation Concern
Refactor: move `destroy` method to Translation Concern
Refactor: abstract internals of `notice_message`