Virtual folders

Firstly here I've implemented missing code for virtual folders - basically the virtual_folders setting in the config didn't do anything so I've made that work.
Secondly I've renamed the "vfolders" option to "virtual_folders_file" and it overrules the "virtual_folders" option.
The reason I left both options in is with the intention that if people want simple virtual folders they can just use "virtual_folders", but if they want complex ones they may want to use several lines and then it makes more sense to use "virtual_folders_file".