PHP files for server-side storage of todo tasks

@erikthedeveloper, @laklein, @TheValencian 

Here are the PHP files as promised. There were a couple of weird things I had to do to get it all working, but we won't worry about those for now. Feel free to comment away!
We should disregard the public properties. It's an artifact of trying to store objects in the session. Non-public properties don't get serialized when calling `json_encode()`. There is some definite refactoring that can happen in the TasksRepository to fix this.