Archival and retrieval jobs are now for individual files

libs/middletier/ArchivalJob.cpp

libs/middletier/ArchivalJob.hpp

libs/middletier/ArchivalJobState.cpp

libs/middletier/ArchivalJobState.hpp

libs/middletier/CMakeLists.txt

libs/middletier/FileArchivalJob.cpp

libs/middletier/FileArchivalJob.hpp

libs/middletier/MiddleTierUser.hpp

libs/middletier/MockMiddleTierUser.cpp

libs/middletier/MockMiddleTierUser.hpp

libs/middletier/RetrievalJob.cpp

libs/middletier/RetrievalJob.hpp

libs/middletier/RetrievalJobState.cpp

libs/middletier/RetrievalJobState.hpp

xroot_plugins/XrdProFilesystem.cpp