Merge branch 'f-multi-retrieve' into f-update

CHANGELOG.md

CMakeLists.txt

include/caosdb/configuration.h

include/caosdb/entity.h

proto

src/caosdb/entity.cpp

test/CMakeLists.txt

test/test_configuration.cpp

test/test_connection.cpp

test/test_entity.cpp

test/test_protobuf.cpp

test/test_transaction.cpp