Simplified the structure of libs directory in order to protect my sanity

libs/CMakeLists.txt

libs/client/API.cpp

libs/client/API.hpp

libs/client/CMakeLists.txt

libs/client/DirectoryEntry.cpp

libs/client/DirectoryEntry.hpp

libs/client/DirectoryIterator.cpp

libs/client/DirectoryIterator.hpp

libs/client/Exception.cpp

libs/client/Exception.hpp

libs/client/MockAPI.cpp

libs/client/MockAPI.hpp

libs/client/MockAPITest.cpp

libs/client/StorageClass.cpp

libs/client/StorageClass.hpp

libs/client/StorageClassList.hpp

libs/ctaclient/CMakeLists.txt

libs/ctacommon/CMakeLists.txt

libs/ctacommon/cta/filesystem/DirectoryConstIterator.cpp

libs/ctacommon/cta/filesystem/DirectoryEntry.cpp