Migration to typescript: first step

Add vue cli typescript support
Rename .js to .ts
Use class and annotations in App and NavBar
Add tslint

js/.eslintrc.js

@@ -1,7 +0,0 @@
-module.exports = {
-  root: true,
-  extends: [
-    'plugin:vue/essential',
-    '@vue/airbnb',
-  ],
-};