Give the web client a major overhaul.
User-visible highlights include:
* Mobile is now fully supported.
* Added fullscreen support on mobile.
* Better support for dark mode.
* Added mime icons to the torrent list.
* Improved theme consistency across the app.
Maintainer highlights include:
* Updated code to use ES6 APIs.
* No longer uses jQuery UI.
* No longer uses jQuery.
* Use Webpack to bundle the Javascript, CSS, and assets together -- the entire bundle size is now 68K gzipped.
* Added eslint / prettier / stylelint tooling.
* Uses torrent-get's 'table' mode for more efficient RPC calls.
