Refactor npm scripts

Per #4147, this adds a new `npm run watch-poll` command, and dries up some of those long repetitive commands.

package.json

@@ -1,10 +1,14 @@
 {
   "private": true,
   "scripts": {
-    "dev": "node node_modules/cross-env/bin/cross-env.js NODE_ENV=development node_modules/webpack/bin/webpack.js --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js",
-    "watch": "node node_modules/cross-env/bin/cross-env.js NODE_ENV=development node_modules/webpack/bin/webpack.js --watch --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js",
-    "hot": "node node_modules/cross-env/bin/cross-env.js NODE_ENV=development node_modules/webpack-dev-server/bin/webpack-dev-server.js --inline --hot --config=node_modules/laravel-mix/setup/webpack.config.js",
-    "production": "node node_modules/cross-env/bin/cross-env.js NODE_ENV=production node_modules/webpack/bin/webpack.js --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js"
+    "dev": "node node_modules/webpack/bin/webpack.js --progress --hide-modules --config=$npm_package_config_webpack",
+    "watch": "npm run dev -- -w",
+    "watch-poll": "npm run dev -- -w --watch-poll",
+    "hot": "node node_modules/webpack-dev-server/bin/webpack-dev-server.js --inline --hot --config=$npm_package_config_webpack",
+    "production": "npm run dev -- -p"
+  },
+  "config": {
+    "webpack": "node_modules/laravel-mix/setup/webpack.config.js"
   },
   "devDependencies": {
     "axios": "^0.15.3",