Tracking: enhancements to auto-save

[mithunshanbhag]

Just creating this umbrella issue to track all enhancement work for the auto-save feature.

• The auto-save status needs to be displayed in the status bar: pending | saved | failed.
• Diagram save request shouldn't get cancelled when switching diagrams (canDeactivate guard).
  • Inside the deactivate guard, we send a save request to the diagram service.
  • However the listener is inside the diagram component which has already been destroyed at this time.
• Investigate using periodic timers for auto-save (say every minute). This would be useful to save any changes for which event callbacks don't exist (note: are there any such events???)
• Show alert if user navigating away when there are unsaved/unpersisted diagram changes.
• Ensure auto-save/PUT requests are not fulfilled out of order.
• Queue up the save requests and process asynchronously (CQRS / queue-based load leveling).
• Debounce all save requests on the client side.
• Ensure that PUT requests do not happen for cosmetic movements (selected symbol changed, zoom level change, user scrolls up/down/right/left on diagram).