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',
-  },
-};

js/tests/unit/HelloWorld.spec.js

@@ -1,13 +0,0 @@
-import { expect } from 'chai';
-import { shallow } from '@vue/test-utils';
-import HelloWorld from '@/components/HelloWorld.vue';
-
-describe('HelloWorld.vue', () => {
-  it('renders props.msg when passed', () => {
-    const msg = 'new message';
-    const wrapper = shallow(HelloWorld, {
-      propsData: { msg },
-    });
-    expect(wrapper.text()).to.include(msg);
-  });
-});