Separation of upload url and path

We needed the ability to distinguish between upload folder URL and upload folder path. The reason for this is that we load our images through our CMS system and thus the path is different from the URL. This fix also makes it possible to specify absolute path for upload folder and thumbnail folder which opens the doors for storing the filemanager source in completely different location.

I hope that you will accept these changes. If you have questions or want something to be done differently, just let me know.