Current behaviour only generate the custom CSS file when the plugin settings are saved, which can be annoying if the file is deleted but the settings are set.
Most common use case is Docker deployment, because the plugin directory is not mounted as a volume.
* 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