[ #7887 ] Prevent most useless object copy

kde/src/AccountListModel.cpp

kde/src/AccountListModel.h

kde/src/AccountView.cpp

kde/src/AccountView.h

kde/src/AkonadiBackend.cpp

kde/src/AkonadiBackend.h

kde/src/CallView.cpp

kde/src/CallView.h

kde/src/Codec.cpp

kde/src/Codec.h

kde/src/conf/ConfigAccountList.cpp

kde/src/conf/ConfigAccountList.h

kde/src/lib/Account.cpp

kde/src/lib/Account.h

kde/src/lib/AccountList.cpp

kde/src/lib/AccountList.h

kde/src/lib/Call.cpp

kde/src/lib/Call.h

kde/src/lib/CallModel.h

kde/src/lib/CallModel.hpp