add first unittest

CMakeModules/testing_cpp.cmake

worker/api/cpp/CMakeLists.txt

worker/api/cpp/include/worker/data_source.h

worker/api/cpp/src/data_broker_factory.cpp

worker/api/cpp/src/folder_data_broker.cpp

worker/api/cpp/src/folder_data_broker.h

worker/api/cpp/unittests/test_worker_api.cpp