[DO NOT MERGE] Spike - Using the public layout components in Static

[maxgds]

This branch is the (ongoing) outcome of spiking implementing the public layout components from the govuk_publishing_components gem. This work was done as part of the drive to reduce legacy and adopt more of the design system across gov.uk to make the site comply better with accessibility standards and to ease the use of the design system and components. This was done by the Frontend and Accessibility mission team which, as of April 2020, is now paused.

The step by step of the work done is documented here:
https://docs.google.com/document/d/1GbuOlFpLxDNFbcC8QbnLdyZBxwu_Bfl5qGcAAXxqCr0/edit#
and it is covered under this ticket:
https://trello.com/c/uEIU7R4m/238-switch-layout-template-for-public-template-in-static

This branch is not intended for merge, but is meant to be a disposable example of an attempt at implementation. At this point tests are failing and haven't been addressed.

The google document linked has more detail but as a TLDR this branch:

• Implements a parallel set of templates that can be called by setting a template variable in a frontend app.
• Pulls in the public layout component from govuk_publishing_components (currently only implemented on a branch) which in turn uses a header and footer component
• Removes chunks of the layout code from static's govuk_template implementation

More work is needed, again outlined in the linked document, mostly around:

• how to ensure all relevant parameters pass through the chain and get rendered, and no spurious code is left outstanding.
• how to apply correct css, removing outdated code and ensuring correct layout, spacing, fonts etc

[injms]

Can we close this pull request? I think it's covered by #2411.

[maxgds]

Closing, superseded elsewhere.