* Change the authentication everywhere to use clouds
   (authentication URL and token pairs)
 * Add menu entries to manage clouds
 * Add an extra -a option in snf-image-creator to allow the user to
   specify authentication URLs

 * Prefix all private methods with _
 * Write missing docstrings
 * Move all public methods above the private ones
 * Add module docstrings where missing
 * Define source code encodings on all modules

If the image gets registered as public allow anyone to read the
metadata and the md5sum file.

Rename DiskDevice class to Image and move it to a seperate module.
Also, don't let the user access the os_type/* modules directly. In
Image class create the `os' member variable that will host an
appropriate instance of one of the OSBase classes.

Create a new dialog_menu module to host all the "expert mode" code.
Check the code with a new version of pep8