feat(core): flatten structure of core package

[piofinn]

affects: @fremtind/jkl-accordion, @fremtind/jkl-bullet-list, @fremtind/jkl-button,
@fremtind/jkl-card, @fremtind/jkl-checkbox, @fremtind/jkl-core, @fremtind/jkl-divider-line,
@fremtind/jkl-dropdown, @fremtind/jkl-footer, @fremtind/jkl-grid, @fremtind/jkl-header,
@fremtind/jkl-logo, @fremtind/jkl-radio-button, @fremtind/jkl-text-input

📥 Proposed changes

Flatten structure of core package as proposed in issue #139

☑️ Submission checklist

• I have read the CONTRIBUTING doc
• yarn build works locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

💬 Further comments

Fixes #139

[lfbergee]

I think this is an improvement. We should clear the PRs before taking on this, as this is a breaking change for the entire project.

Also checkout the _index.scss file instead of _variables.scss and _mixin.scss

[lfbergee]

Also cpx, ncp depdendencies can be deleted

[piofinn]

Also checkout the _index.scss file instead of _variables.scss and _mixin.scss

Not possible yet in node-sass as of yet (new feature in LibSass from May)

We should clear the PRs before taking on this, as this is a breaking change for the entire project.

Yep. All existing packages have their imports updated here, but we should consolidate all the incoming changes as well.