implement backend api v2

dist/bundle.js

dist/checkin.html

dist/checkout.html

src/js/auth.js

src/js/checkin.js

src/js/checkout.js

src/js/main.js

src/js/scanner.js

src/js/tag.js

src/js/util.js

src/views/checkin.html

src/views/checkout.html

src/views/components/foot.html