Icon handling

[dreamos82]

The basic icon handling is done now, but there are still things to do:

1. Decide where to position of the icon
2. Decide the default size of the icon and if it has to be fixed or there could be different options avaiable
3. Understand why if the icon Window is displayed before the text Window this one doesn't appear.
4. At the moment only the default icon is loaded by the window manager, but ideally the appications can provide their own icons, so if those are available they should be loaded instead.
5. Could be useful to look for the icons in a set of default folders (need to understand how to associate an icon with an application)
6. Maybe the user should be able to disable them