Fix failure to load files in archive root (new bug)

With this update dweb should be able to publish from Linux and Windows (and Mac) and to visit sites published or uploaded from any OS. Archives uploaded using ant file upload -p should also be supported.

This required handling of forward and backwards path separators in the paths in an archive. There is an issue open (maidsafe/autonomi#3042) requesting that Autonomi standardise this so future apps don't have to handle both when accessing Archives.