Zipped downloads are broken

[jamiesnape]

• in core/controllers/DownloadController.php the autoload fails:
  all new ZipStream allocations should be new ZipStream\ZipStream
• same file, rename all calls add_file_from_path to addFileFromPath as that's the name of the method in ZipStream. Similar for add_file into addFile
• repeat in core/models/pdo/FolderModel.php as you're operating on a ZipStream object. Perhaps rename the zipStream function into zipStreamWrapper or something more suggestive to avoid looking too hard for a lowercase vs uppercase Z 😄
• rinse and repeat in modules/remoteprocessing/controllers/AdminController.php and
  modules/keyfiles/controllers/DownloadController.php

— @cfarcas