modernize js and use babel (#8973)

* modernize js and use babel

- add babel toolchain to transform modern JS to ES5
- extend eslint config for modern rules
- fixes linting issues via `eslint --fix` and manual fixes

* run 'make css' to satisfy CI

* code style tweaks and set js indendation to 2 in .editorconfig

* regenerate js

webpack.config.js

@@ -9,12 +9,34 @@ module.exports = {
   devtool: 'source-map',
   output: {
     path: path.resolve(__dirname, 'public/js'),
-    filename: "[name].js"
+    filename: '[name].js'
   },
   optimization: {
     minimize: true,
-    minimizer: [new TerserPlugin({ 
-        sourceMap: true
-     })],
+    minimizer: [new TerserPlugin({
+      sourceMap: true,
+    })],
   },
+  module: {
+    rules: [
+      {
+        test: /\.js$/,
+        exclude: /node_modules/,
+        use: {
+          loader: 'babel-loader',
+          options: {
+            presets: [
+              [
+                '@babel/preset-env',
+                {
+                  useBuiltIns: 'entry',
+                  corejs: 3,
+                }
+              ]
+            ]
+          }
+        }
+      }
+    ]
+  }
 };