Add stylelint

package.json

@@ -12,6 +12,7 @@
     "file-loader": "^3.0.1",
     "html-webpack-plugin": "^3.2.0",
     "style-loader": "^0.23.1",
+    "stylelint": "^13.0.0",
     "webpack": "^4.41.0",
     "webpack-cli": "^3.3.9",
     "webpack-concat-plugin": "^3.0.0",
@@ -26,6 +27,7 @@
     "howler": "^2.1.2",
     "jquery": "^3.4.1",
     "jstree": "^3.3.7",
+    "libass-wasm": "^2.1.1",
     "libjass": "^0.11.0",
     "native-promise-only": "^0.8.0-a",
     "requirejs": "^2.3.5",
@@ -33,7 +35,6 @@
     "shaka-player": "^2.5.5",
     "sortablejs": "^1.9.0",
     "swiper": "^3.4.2",
-    "libass-wasm": "^2.1.1",
     "webcomponents.js": "^0.7.24",
     "whatwg-fetch": "^1.1.1"
   },