upgrade to webpack 4 - complete overhaul

app/pages/not-found/not-found.tsx

@@ -0,0 +1,18 @@
+import React from 'react';
+import { RouteComponentProps } from 'react-router-dom';
+
+import './not-found.scss';
+
+interface Props extends RouteComponentProps<any> {}
+
+interface State {}
+
+export class NotFound extends React.Component<Props, State> {
+  constructor(props: Props) {
+    super(props);
+  }
+
+  public render(): JSX.Element {
+    return <div className="not-found">404 Not Found</div>;
+  }
+}