Migrate to webpack 4.8 and use proper jquery timepicker

Signed-off-by: Julius Härtl <jus@bitgrid.net>

js/webpack.prod.config.js

@@ -1,13 +1,15 @@
 const webpack = require('webpack');
 const merge = require('webpack-merge');
 const baseConfig = require('./webpack.config.js');
+const UglifyJsPlugin = require('uglifyjs-webpack-plugin')
+
 
 module.exports = merge(baseConfig, {
-	plugins: [
-		new webpack.DefinePlugin({
-			'process.env': {
-				'NODE_ENV': JSON.stringify('production')
-			}
-		}),
-	]
-});
+  mode: 'production',
+  optimization: {
+    minimizer: [
+      new UglifyJsPlugin({
+        test: /(vendor\.js)+/i
+      })
+    ]
+  }});