Clearer change notes for admin

• Update copy and styling, and reorder elements re new design
• Add placeholder text

https://www.pivotaltracker.com/story/show/56857726
Adds JS layer to edition change notes fieldset
Org transition visualisation controlled by feature flag
Rename feature flag initializer file

we want to be able to selectively override particular feature flags
from the deploy scripts, so each feature flag should have its own
initializer file
Merge pull request #1023 from alphagov/feature-flag-for-govuk-status-bar

Org transition visualisation controlled by feature flag

https://www.pivotaltracker.com/story/show/59480970
Merge pull request #1003 from alphagov/clearer-admin-change-notes

Clearer change notes for admin

https://www.pivotaltracker.com/story/show/56857726
Prevent intermittent test timing issues

We use this function to open preview links (or other links which would
normally open in a new tab) because capybara does not support following
links which open a new browser window. When using the javascript enabled
driver (poltergeist) there can be timing issues if we don't wait for the
page to load before attempting to click the preview link.

Adding this `page.has_css?` ensures that capybara waits for that link to
be present on the page before proceeding to try to open the link.
Merge commit 'c3db531218326e93bcf8ee5dff8b8a198f5a20a0' into HEAD