Mostly in order to get rid of deprecated deps, and upgrade vulnerable ones.
- Upgrade webpack from 3.x to 4.x
- Moved babel package to main repo
- Replaced deprecated extract-text-webpack-plugin with extract-text-webpack-plugin
- Replaced deprecated babel-minify-webpack-plugin with terser-webpack-plugin
- Replaced deprecated node-sass with (dart) sass package
- Replaced deprecated sass-lint with stylelint (the rules might be a bit different
Related to #1531: trivy doesn't raise any more issue
* Adds a new core plugin to override default template colors
* Adds a new hook when plugin settings are saved
(`save_plugin_parameters`)
* Use CSS native variables for main colors instead of SASS variables
* Disable SASS sort order rules due to a bug in the plugin
Fixes#1312
