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.
Display delete important note alongside buttons

* Prevent wrapping using a new helper class
Integration tests for new important_note behaviour
Bump govuk_content_models version
Merge pull request #277 from alphagov/important_notes

Audit trail for important notes
Bump jasmine gem

*
https://github.com/pivotal/jasmine-gem/blob/master/release_notes/v2.0.3.
md
Get Select2 assets from gem

* Update to version 3.5.0 of Select 2
* Update Bootstrap 3 Select2 style overrides
* Apply site wide in preparation for user select improvements
  * Remove specific business support javascript includes and styles
Add form-control class to select2 element

* The select2 overrides are more specific and only apply fixes to
elements with a form-control class. Normally this is passed through to
the select2 widget but the business support script is generating a
hidden input
* Add form-control to the hidden input when it’s created
Fix alignment of checkboxes on business support

* Checkboxes were using a markup pattern from Bootstrap 2 that appears
to have broken with a Boostrap 3.2 upgrade
* Use the recommended pattern from
http://getbootstrap.com/css/#forms
Enhance user select drop down with select2

* Allow users to search the list of users instead of having to scroll
up and down