refactor code

minor fix

FE integration code changes

refactor code: 1)replace mysql with promise based mysql2; 2)restructured project, introduced service layer; 3)enabled API docs with swagger ui

1) added more i18n words; 2)fixed multiple http request issue caused by response body; 3)added user login validation when adding sth to cart;4)now user could not revist checkout page after checkout complete

modified README

1) enabled email address verification with node-mailer; 2) refactored some code; 3) Added some auth APIs

1)Introduced Controllers to re-write APIs; 2)fixed issue causing same email could be registered multi times;

updated repo description

front-end code has been split to client branch, with new features added

Delete .DS_Store

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1) splited client & server 2)deployed to netlify & heroku for free