implemented getlast, getbyid for datasets

broker/src/asapo_broker/database/mongodb_test.go

common/cpp/include/common/data_structs.h

examples/worker/getnext_broker/getnext_broker.cpp

...orker/next_multithread_broker/next_multithread_broker.cpp

...orker/next_multithread_folder/next_multithread_folder.cpp

tests/automatic/worker/worker_api/check_linux.sh

tests/automatic/worker/worker_api/worker_api.cpp

worker/api/cpp/include/worker/data_broker.h

worker/api/cpp/src/folder_data_broker.cpp

worker/api/cpp/src/folder_data_broker.h

worker/api/cpp/src/server_data_broker.cpp

worker/api/cpp/src/server_data_broker.h

worker/api/cpp/unittests/test_folder_broker.cpp

worker/api/cpp/unittests/test_server_broker.cpp