Add corejs: 3, and pull out babel config from webpack config (#84)

* add `corejs: 3` and pull out babel config from webpack config

* typo

webapp/webpack.config.js

@@ -19,33 +19,9 @@ module.exports = {
                 use: {
                     loader: 'babel-loader',
                     options: {
-                        plugins: [
-                            '@babel/plugin-proposal-class-properties',
-                            '@babel/plugin-syntax-dynamic-import',
-                            '@babel/proposal-object-rest-spread',
-                            'babel-plugin-typescript-to-proptypes',
-                        ],
-                        presets: [
-                            ['@babel/preset-env', {
-                                targets: {
-                                    chrome: 66,
-                                    firefox: 60,
-                                    edge: 42,
-                                    safari: 12,
-                                },
-                                modules: false,
-                                debug: false,
-                                useBuiltIns: 'usage',
-                                shippedProposals: true,
-                            }],
-                            ['@babel/preset-react', {
-                                useBuiltIns: true,
-                            }],
-                            ['@babel/typescript', {
-                                allExtensions: true,
-                                isTSX: true,
-                            }],
-                        ],
+                        cacheDirectory: true,
+
+                        // Babel configuration is in babel.config.js because jest requires it to be there.
                     },
                 },
             },