EHN: implement copy constructors and release methods

CMakeLists.txt

conanfile.py

include/caosdb/entity.h

include/caosdb/message_code.h

include/caosdb/status_code.h

include/caosdb/transaction.h

include/caosdb/transaction_status.h

src/caosdb/entity.cpp

src/caosdb/status_code_description.cpp

src/ccaosdb.cpp

test/test_transaction.cpp