Convert application entrypoint files into Typescript

app/application.ts

@@ -0,0 +1,14 @@
+import loadPolyfills from './soapbox/load_polyfills';
+
+// @ts-ignore
+require.context('./images/', true);
+
+// Load stylesheet
+require('react-datepicker/dist/react-datepicker.css');
+require('./styles/application.scss');
+
+loadPolyfills().then(() => {
+  require('./soapbox/main').default();
+}).catch(e => {
+  console.error(e);
+});