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/tests/unit/.eslintrc.js

@@ -1,8 +0,0 @@
-module.exports = {
-  env: {
-    mocha: true,
-  },
-  rules: {
-    'import/no-extraneous-dependencies': 'off',
-  },
-};