Dart Web Server

    Get all users
    GET
    http://127.0.0.1:4000/get

        [
        {"id": "","name":"X","age":11,"photo_url":"http://xyz.png"},
        ...
        ]
    
    Add new user
    POST
    http://127.0.0.1:4000/add
        body => {"addUser":{"name": "",...}}

    Update a user
    POST
    http://127.0.0.1:4000/update
        body => {"updateUser":{"id":"","name":"",...}}

    Delete a user
    DELETE
    http://127.0.0.1:4000/delete
        body => {"deleteUser":{"id":""}}