WebDAV: Configure and use server-side filesystem adapter

Unlike WebDAV client, in TEWebDAVServer there's no default filesystem adapter created. Before you start the server, you need to assign the instance of the filesystem adapter to TEWebDAVServer.FileSystemAdapter property. It can be an instance of TElDiskFileSystemAdapter, SolFS adapter or other descendant of TElCustomFileSystemAdapter. If you create your custom filesystem adapter, be sure that WriteFileTag(), ReadFileTag() and DeleteFileTag() methods of the adapter are implemented.