Add SCSS errors to CodeInspection, support basic selectors in Quick Edit

* Big refactoring to separate compiler, source maps and live preview agent
* Show limited compile errors reported by node-sass
    * For the main input file, errors within partials are rolled up to the main file
    * Errors in partials will also show up when editing the partial itself
* ALPHA support for Quick Edit
    * Fails to handle parent selector `&`
    * Does not properly detect ending curly brace `}` when using nested styles