Improved sessions, data classes, IO

Removed JSON database.
Removed duplication of dataSource method calls in the Model class.
Created new method, areRolesAllowed.
Rearranged the open method in the json file storage class.
Rearranged the display method in the flash service.
Used anonymous function for default value in the setOnFormat method in
the flash service.
Created method, getUnusedId, in the session manager.