multitasking for folder_db_importer

3d_party/mongo-c-driver/install.cmd

CMakeLists.txt

common/cpp/include/database/database.h

common/cpp/include/database/mongodb_client.h

common/cpp/src/database/mongodb_client.cpp

worker/tools/folder_to_db/src/folder_db_importer.cpp

worker/tools/folder_to_db/src/folder_db_importer.h

worker/tools/folder_to_db/src/main.cpp

worker/tools/folder_to_db/unittests/test_folder_to_db.cpp