Added the UserRequest class and its sub-classes

middletier/CMakeLists.txt

middletier/cta/ArchivalRequest.cpp

middletier/cta/ArchivalRequest.hpp

middletier/cta/ArchivalRequestHandler.hpp

middletier/cta/ArchiveToDirRequest.cpp

middletier/cta/ArchiveToDirRequest.hpp

middletier/cta/ArchiveToFileRequest.cpp

middletier/cta/ArchiveToFileRequest.hpp

middletier/cta/RetrievalJobQueues.hpp

middletier/cta/RetrievalRequest.cpp

middletier/cta/RetrievalRequest.hpp

middletier/cta/RetrieveToDirRequest.cpp

middletier/cta/RetrieveToDirRequest.hpp

middletier/cta/RetrieveToFileRequest.cpp

middletier/cta/RetrieveToFileRequest.hpp

middletier/cta/UserRequest.cpp

middletier/cta/UserRequest.hpp