Prepare the DOM for inline article upgrades

Also added a feature switch.
Clearer test wording
Add a list of paragraphs to the model

This is so any trail can be expanded inline.
Output the first four paragraphs of an article (rather than a standfirst) in the story package
Fix failing test
Change the language of the Trail interface to include leadingParagraphs.
Some content types are bodyless.
Fall back to regular trail style when body not available for long trail form.
Body shouldn't come up to Content, my bad.
fix trailblock hide/show
Tweaked swipe bar interaction behaviour
Refactored css transition to use mixin
Moved header magic number intl variable
Merge pull request #1393 from guardian/swipe-ctas

Tweaked swipe bar interaction behaviour
fix fixtures appearing in masthead component
move trailblock show more into trailblock
hash to opt in/out of facia
Update CONTRIBUTING.md
Merge pull request #1394 from guardian/fronts-front-fixes

Facia fixes
Remove scroll reset on flip