Online diagram editor +/- user sign-in ability

I am trying to create a website for students and doctors to be able to sign-in to make and edit Flow diagrams on the website.

I have already found JsPlumb from http://jsplumb.org/jquery/demo.html that does the linking for the flowchart boxes

I am looking for a web-programmer who can:
1. Program a site so that it enables users to login.
2. Store JsPlumb's positional data when saving so that to be able to retrieve it later.
3. allow user to add and remove boxes and endpoints(endpoints is from JsPlumb).

I have already made a prototype of the website that I am trying to make and here is what I want the end flow-diagram to look like. (I made this using powerpoint and uploaded as a .png file)

http://hexaxell.com/image/medicine/image/gastroenterology/liver%20abscess/liverabscess.html

Although I am paying this from my own pocket, I am will be happy to discuss the final amount as long as the work is up to my expectations