Save-upload functionality

On save we get from Dynamo all workspaces that were loaded - home workspace (ws) and all custom nodes' workspaces.

We can load file of home ws (*.dyn) or custom node ws (*.dyf). 

New concept here is proxy node. It's a custom node that hasn't its own definition (corresponding ws). If we load a ws with a custom node instance before we load custom node definition this node will be marked as proxy. Then after loading the custom node' ws this node will stop being proxy.
Just make this - "Save" and "Open".  Consider adding an icon from font-awesome.  The Workspaces button should not be visible in Dynamo/Flood.