gPodder Configuration Editor

I've had the idea of implementing some kind of about:config-like configuration editor for gPodder for some time now. Not only does it give a nice live view of the current configuration settings, it also makes it possible to edit some configuration values that were previously only available by editing ~/.config/gpodder/gpodder.conf by hand.

Apart from that, we might be able to strip down the preferences dialog to only the really important settings and leave everything else in the "advanced" configuration editor :) I think the interface is quite nice and even looks nicer than the real about:config editor. As with Mozilla's about:config editor, this also marks the settings that have been modified from their default value in bold.