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/src/shims-tsx.d.ts

@@ -0,0 +1,13 @@
+import Vue, { VNode } from 'vue'
+
+declare global {
+  namespace JSX {
+    // tslint:disable no-empty-interface
+    interface Element extends VNode {}
+    // tslint:disable no-empty-interface
+    interface ElementClass extends Vue {}
+    interface IntrinsicElements {
+      [elem: string]: any
+    }
+  }
+}