Switch from webpacker to (css|js)bundling-rails (#227)

* Install jsbundling-rails, uninstall rails/webpacker
* Remove outdated step from run-tests workflow
* Use cssbundling-rails for CSS

config/webpack/webpack.config.js

@@ -0,0 +1,53 @@
+const path    = require("path")
+const webpack = require("webpack")
+
+const mode = process.env.NODE_ENV === 'development' ? 'development' : 'production';
+
+module.exports = {
+  mode: mode,
+
+  optimization: {
+    moduleIds: 'deterministic',
+  },
+  entry: {
+    application: "./app/javascript/application.js"
+  },
+  output: {
+    filename: "[name].js",
+    sourceMapFilename: "[file].map",
+    path: path.resolve(__dirname, "..", "..", "app/assets/builds"),
+  },
+  resolve: {
+    extensions: ['.js', '.jsx', '.ts', '.tsx'],
+  },
+  module: {
+    rules: [
+      {
+        test: /\.(js|jsx|ts|tsx)$/,
+        exclude: /node_modules/,
+        use: ['babel-loader']
+      },
+      {
+        test: /\.erb$/,
+        enforce: 'pre',
+        exclude: /node_modules/,
+        use: [{
+          loader: 'rails-erb-loader',
+          options: {
+            runner: (/^win/.test(process.platform) ? 'ruby ' : '') + 'bin/rails runner'
+          }
+        }]
+      }
+    ]
+  },
+  plugins: [
+    new webpack.optimize.LimitChunkCountPlugin({
+      maxChunks: 1
+    }),
+    new webpack.ProvidePlugin({
+      $: 'jquery',
+      jQuery: 'jquery',
+      Popper: ['popper.js', 'default']
+    })
+  ]
+}