File Load and Save.

[gabyx]

• [x] Backend (master) saves and loads the graph to the m_rootPath of the filesystem (given at startup)
• [x] open,save-Component calls the service to save/load the graph and delivers in the case of save the serialized visualization flatbuffer (backend has no knowledge about this buffer). Backend serializes the graph and the visualization buffer into file schema ExecutionGraph.fbs
• [ ] Client: Save Implement the Visualization serialization
  • What should we serialize (Pos. of nodes. etc...)
• [ ] Client: Load Implement how and where we setup all visualization properties (model.Node.uiProps, model.Connection.uiProps model.Graph.uiProps?. Maybe an effect: UpdateVisProps... for the corresponding models data structures...? So after LoadGraph we dispatch the UpdateVisProps ??

[gabyx]

Branch: feature/file-load-save