Replace deprecated node-sass dependency with dart-sass

[0xdevalias]

fixes #850

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From #850:

• Move away from node-sass and update documentation related to it facebook/create-react-app#10045 (comment): dart-sass is the default option in sass-loader. So what you need to do it's just install sass and it will work. Docs regarding it should be updated

  • 9.0.0 (2020-07-02): https://github.com/webpack-contrib/sass-loader/blob/master/CHANGELOG.md#900-2020-07-02

    • prefer sass (dart-sass) by default, it is strongly recommended to migrate on sass (dart-sass)

  • 7.2.0 (2019-08-08): https://github.com/webpack-contrib/sass-loader/blob/master/CHANGELOG.md#720-2019-08-08

    • support auto resolving dart-sass

• https://github.com/facebook/create-react-app/blob/v3.4.4/packages/react-scripts/package.json#L73

  • "sass-loader": "8.0.2"

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Since we already seem to be using a version of saas-loader that supports the non-deprecated dart-sass, and because create-react-app's react-scripts doesn't seem to support node-sass v5 yet (targeted for 4.0.2 milestone), I think our best way forward here is to switch to using dart-sass instead of this.

Originally posted by @0xdevalias in #1079 (comment)

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