Theme updates - breadcrumbs, side and mobile navigation.

Please review / merge https://github.com/ministryofjustice/justice-gov-uk/pull/46 first. It will simplify the files changed for this PR, as this branch is based off theme-updates.

Simplify the content-wrapper css with display:flex
Remove page-left-centre-right because that template is used for 99% of pages, and is better to be the default.
Add body classes to match squiz html
Add breadcrumbs class and template part.
Breadcrumbs can use short_name metadata. Similar behaviour to squiz dashboard.
Create Meta class for shortTitle.
Add mobile nav to footer.

ministryofjustice / justice-gov-uk