added Torrent.PACK media type. PACK is derived from Torrent.MOVIE. It is used for movie packs that contain a collection of movies.

added self.parent MediaBuilder class member, gathered from new optional argument. used in conjunction with Torrent.PACK.

collect_metadata() has been updated to take advantage of Torrent.PACK. now branches and spins off its own instance of MediaBuilder in a for-loop iteration.

verify_source_data() updated to handle self.parent existence with Torrent.PACK. if the calling instance is from a Torrent.PACK (read: self.parent is not None), self.name is set to concatenation of self.parent and self.name for directory traversal.

in verify_source_data() sorted() modifier is fixed to handle Torrent.PACK.

updated build_media() to take advantage of Torrent.PACK.