make worker lib thread-safe

CMakeModules/testing_cpp.cmake

doxygen.ini

tests/CMakeLists.txt

tests/common/cpp/include/testing.h

tests/common/cpp/src/testing.cpp

tests/worker/CMakeLists.txt

tests/worker/connect_multithread/CMakeLists.txt

tests/worker/connect_multithread/cleanup.sh

tests/worker/connect_multithread/content_multithread.cpp

tests/worker/connect_multithread/setup.sh

tests/worker/next_multithread/CMakeLists.txt

tests/worker/next_multithread/cleanup.sh

tests/worker/next_multithread/next_multithread.cpp

tests/worker/next_multithread/setup.sh

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/unittests/test_folder_broker.cpp