Add migration to import taggings from panopticon.

Requires bump to govuk_content_models.
Remove video fields from non-video formats

* Video url and summary fields aren’t used, they just clutter the
edition form
* There are only 10 published videos, all in the video format
Remove video icons from table list

* Only video formats will have videos, and that’s guessable from the
format type alone
Use input helper classes for video fields

* Avoid using grid wrappers, the admin gem provides helpers for setting
the maximum width of form elements
Use input helper classes on common attributes

* Avoid using divs as grid wrappers to restrict width of form elements.
The admin gem provides classes for this.
* Remove beta help text, the explanation is extraneous now the feature
has been introduced and understood
Use input helper classes on business support form

* Constrain widths using classes rather than grid wrappers
Whitespace: alignment of tags in business support
Use input helper classes on campaign form
Use input helper classes on answer form
Use input helpers on remaining forms

* Tidy up whitespace for input attributes
* Use more rows for introductory paragraphs (2 isn’t enough for most
content, scrolling the small boxes is painful)
Merge pull request #276 from alphagov/import-topic-taggings-from-panopticon

Add migration to import taggings from panopticon.
Add a debugger.
Whitespace.
Allow tagging of editions to mainstream browse pages.
Allow tagging of editions to topics.
Provide clearer indication of primary browse page.

Copy is from the Panopticon interface.
Move tag fields beneath main content

Tags don’t change too often, so the fields, which are more complex than
simple text inputs, shouldn’t obscure the main content ones.

* Move tags into a partial
* Put partial at the bottom of each form
* Add a tags header and divider to separate fields from rest of form
Cleanup spacing of tag fields

* Use a smaller grid width to match earlier form fields
* Nest each item in a form-group for vertical spacing
* Re-word the section explanation
Avoid poltergeist overlay problems

Now the smart answer buttons are not at the bottom of the page, the
fixed workflow buttons obscure them when automating a click.

* Use trigger instead of click_on to always trigger the click on the
right element and avoid poltergeist’s co-ordinate warning
Lock the collections inputs on locked resources.