change design

See merge request kiran/todo-app-jan-schnaidt-and-abdullah-kiran!1

remove todoId from todo and todo-list from user, remove todo-list from login-page, remove todo-id from main-page

move authentication check to userservice, add test for usercontroller, add login method to userservice

add user authentication, add user controller, add signup and login endpoints, add salting and hashing method, add setup to userservicetest