Move template from the core layer to the objects layer

[36degrees]

What

Move the template styles from core/_template.scss to objects/_template.scss, so that we treat it as an object rather than core styling.

Why

As proposed in alphagov/govuk-design-system-architecture#22, we’re making changes to the way that the base layers (settings, tools and helpers) are imported within different parts of GOV.UK Frontend’s Sass, to reduce the time it takes to compile to CSS.

We think that template is the only thing currently in the core layer that you might want to import using a single entry point, e.g. in contexts such as React. Rather than giving it 'special treatment', we can move it to the objects layer and then apply consistent approaches within each layer.

Done when

• TBC
• "Details of breaking change" section below completed to help with writing release notes

Details of breaking change

• which users are affected: TBC
• the change that’s been made: TBC
• changes users will have to make: TBC
• impact of users not making those changes: TBC