Saving workspace functionality

Saving workspace functionality:
- the Dynamo receives a message about saving, saves all workspaces as files and sends them back to the Flood.

Part of changes that had to be uploaded with "Changing the way of geometry transmission" but wasn't:
- receiving a geometry message, process it and send back the geometry data

Enhancements of the code (there is not a lot of them, so I add them into this PR):
- checking for not null, correct guid, removing old code, etc
Does it matter to Flood that all the custom nodes have no names and they all end up as ```MyCustomNode.dyf```? If that doesn't matter, then perhaps we don't have to really use a real file name. We can make use of some .NET API to generate temporary file path+name, then save/delete the temporary file.