Improve folder config dialog:
* rewrite all things from the old KGet and improve it
* respect the default folder config when adding a new download

All is working fine for me, but I have two small problems:
* saving the list does happen for now after every change. I got it not working with Apply / Ok buttons. That means that after a list change the Apply button is not enabled.
* KConfigDialogManager complains about for example buttons in the config dialog:
kdecore (KConfigDialogManager): Widget 'removeButton' (QPushButton) remains unmanaged.
Any hints would be welcome ;)