Uploading workspace functionality

The Dyname receives a file as byte array, saves it as a file, upload this file, sends all needed for restoring the workspace data to the Flood
This ```GetFileName``` method belongs to ```UploadFileMessage``` class, please move it there and make it ```private static``` if possible. Then expose two new read-only properties in ```UploadFileMessage```: ```string FileName```, and ```bool IsCustomNode```.