The app.server property, and simple authentication.

Hi Vitali,
I like your works.

This pull request is for add the **server** property to the app object. This property is the server path for all ajax comunications, or none if there is not an ajax comunication (client only).

Also I have implemented a simple session tracking on server/php for test it. login.php, logout.php and user.php.
The folder server/php/sessions must have write permissions and manage all sessions files. There are only one posible session for user, and the session id and filename is the user name.