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/constants.ts

@@ -0,0 +1,3 @@
+export const AUTH_TOKEN = 'auth-token';
+export const AUTH_USER_ID = 'auth-user-id';
+export const AUTH_USER_ACTOR = 'auth-user-actor';