WIP: files

src/caosdb/file_transmission/DownloadRequestHandler.cpp

src/caosdb/file_transmission/FileReader.cpp

src/caosdb/file_transmission/FileWriter.cpp

src/caosdb/file_transmission/LICENSE

src/caosdb/file_transmission/UploadRequestHandler.cpp

...caosdb/file_transmission/register_file_upload_handler.cpp

src/caosdb/transaction.cpp

src/caosdb/transaction_handler.cpp

src/caosdb/unary_rpc_handler.cpp

test/test_file_transmission.cpp

test/test_transaction.cpp