[gDesklets] Better handling of <enum> and <list> in prefs dialog

[Ronny Lorenz <raumzeit gmx net>]

Here is a link to the changes I propose for the prefs dialog. I outlined 
the 'new' behavior in blueprint 
http://blueprints.launchpad.net/gdesklets/+spec/prefs-items-handling

http://www.sendspace.com/file/mbtzgc

This link points to a gzipped tar archive where I put the patches for 
config/ConfigList.py and config/ConfigEnum.py as well as a testing 
desklet. The latter does nothing else then demonstrating the behavior of 
the prefs dialog on item changes of those both elements.