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.
Do you mean `guid`? I added it on purpose because it needs to know whether we have a workspace for a custom node or not. Mongo generates `_id` as big int number, not as Guid (as Dynamo does). So this two fields are different. 
Ideally to use only `_id` field and generate it in guid view but it causes to a lot of changes through the project because int `_id` is used. So my suggestion is to leave `guid` for now