WIP: upload/download files

caosdb-proto

pom.xml

.../org/caosdb/server/grpc/EntityTransactionServiceImpl.java

...java/org/caosdb/server/grpc/FileDownloadRegistration.java

src/main/java/org/caosdb/server/grpc/FileTransmission.java

...a/org/caosdb/server/grpc/FileTransmissionServiceImpl.java

...n/java/org/caosdb/server/grpc/FileUploadRegistration.java

src/main/java/org/caosdb/server/grpc/GRPCServer.java

src/main/java/org/caosdb/server/grpc/UploadBuffer.java