Replace node-sass with dart-sass

[ThaNarie]

• https://github.com/sass/dart-sass
• https://webpack.js.org/loaders/sass-loader/

The data option of sass-loader is not yet supported anymore, so no more auto-global imports. Which means that each scss file should now import seng-scss and the globals itself.

Suggestion is to move the seng-scss import into the globals file, and import that on top of each file - and add it to the templates.

Steps:

• uninstall node-sass
• install sass and fibers
• update sass-loader to latest version (compatible with webpack 4)
• remove data option in webpack config for sass-loader
• add import to src/app/style/global in each file, and the template(s)
• test if it still works

[jesse-mm]

• [x] node-sass-json-importer is compatible with dart-sass importer option
• [x] tested variables (global import)
• [x] tested with seng-scss functionality respond-to
• [x] tested by running a build and preview it