Merge branch 'clean_mongo_cpp' into 'develop'

broker/src/asapo_broker/database/mongodb.go

broker/src/asapo_broker/database/mongodb_streams.go

broker/src/asapo_broker/database/mongodb_test.go

broker/src/asapo_broker/server/get_commands_test.go

broker/src/asapo_broker/server/get_streams.go

common/cpp/include/asapo/database/database.h

common/cpp/include/asapo/unittests/MockDatabase.h

common/cpp/src/database/mongodb_client.cpp

common/cpp/src/database/mongodb_client.h

producer/api/cpp/src/producer_impl.cpp

producer/api/cpp/src/producer_impl.h

producer/api/cpp/unittests/test_producer_impl.cpp

receiver/CMakeLists.txt

receiver/src/request_handler/request_factory.cpp

receiver/src/request_handler/request_factory.h

.../src/request_handler/request_handler_db_delete_stream.cpp

...er/src/request_handler/request_handler_db_delete_stream.h

receiver/src/request_handler/request_handler_db_get_meta.cpp

receiver/src/request_handler/request_handler_db_get_meta.h

...er/src/request_handler/request_handler_db_last_stream.cpp