The FilePickerAction drives the FilePicker helper.
This works with the ResourcesTool to show a file picker / attachment editor that can be used by any Sakai tools as a helper.
If the user ends without a cancel, the original collection of attachments is replaced with the edited list - otherwise it is left unchanged.
Inner class encapsulates information about resources (folders and items) for editing
This is being phased out as we switch to the resources type registry.