add sign up page

see this url: http://host:port/sign-up

some questions about the front-end:

1. login is using `POST /api/auth`. how about registering? I temporary use `PUT /api/auth` to create a user. It seems not obey the restful rules...
2. how to seperate the page which need login in or not? I see a `if ... else` in the `/public/js/routes/index.js`, maybe it should have something like a filter before routing?