Make application CSS/JS extend header_footer_only CSS/JS

All of the CSS/JS modules included in the application 'layout' are
also included in header_footer_only - and only those modules - so
this makes application share exactly those modules by importing
header footer only.

This helps avoid bugs like https://github.com/alphagov/static/pull/458

Also by treating each layout as an extension of an existing layout,
layering new features on top, then we can easily add new kinds
of layout in the future.
Added a class to the loading paragraph and updating styling to class
instead of generically all child paragraphs of .loading

• update p to class next-step (currently unique class in static)

https://www.agileplannerapp.com/boards/105200/cards/5835
Merge pull request #463 from alphagov/fix-smartanswers-jittery-paragraphs

Added a class to the loading paragraph (smartanswers) and updating styling to match
Merge pull request #461 from alphagov/layout-inheritance

Make application CSS/JS extend header_footer_only CSS/JS
Add comment to conditionals2.scss

- If this mixin is removed in the future it may also need removing from smartanswers application.scss
Merge pull request #465 from alphagov/add-comment-to-conditionals2

Add comment to conditionals2.scss
Bump frontend toolkit and template

Which includes the latest updates for reset the font for print
stylesheets. Which is a font fix for browser and printer issues
reported by users.

https://www.agileplannerapp.com/boards/105200/cards/4633
Merge pull request #467 from alphagov/bump-template-version

Bump frontend toolkit and template