Merge branch 'f-files' into 'dev'

include/caosdb/utility.h

include/ccaosdb.h

proto

src/CMakeLists.txt

src/caosdb/connection.cpp

src/caosdb/entity.cpp

src/caosdb/file_transmission/download_request_handler.cpp

src/caosdb/file_transmission/file_reader.cpp

src/caosdb/file_transmission/file_writer.cpp

...caosdb/file_transmission/register_file_upload_handler.cpp

src/caosdb/file_transmission/upload_request_handler.cpp

src/caosdb/logging.cpp

src/caosdb/protobuf_helper.cpp

src/caosdb/transaction.cpp

src/caosdb/transaction_handler.cpp

src/caosdb/unary_rpc_handler.cpp

src/ccaosdb.cpp

test/CMakeLists.txt

test/caosdb_test_utility.h.in

test/test_ccaosdb.cpp