Intersect DEVSUPPORT-1180: Fix folder drag and drop issues

1. Drag and drop of items in the tree does not work properly, you can only drag to the top of the list and just before or after a virtual 'folder' - Fixed, you can not drag onto a non-folder node. Otherwise you can drag to anywhere: inside top or bottom of a folder, after or before a folder
2. Moving items does not automatically save to the manifest on the server (this shows up when you download as EPUB, may not be obvious if that's not turned on) - Fixed