[Project] Save & restore current graph

[kmcginnes]

Today, Graph Explorer scenes are per session. Meaning, if you refresh the browser, or close and reopen the browser, you will start over with an empty graph.

Launching Graph Explorer should resume the previously active graph.

Potential Issues

• Node and edge IDs may no longer exist since graph was saved
• Connection may have changed since graph was saved
• Cascade of database queries may be taxing on the server

Related Issues

• Follow up #440
• Follow up #586

Tasks

• [ ] [Task] Add explorer function to get node details by ID
• [ ] [Task] Add explorer function to get edge details by ID
• [ ] [Task] Persist snapshot per connection on every change
• [ ] [Task] Cascade delete snapshot when connection is deleted
• [ ] [Task] Reload snapshot on app initialization
• [ ] [Task] Reload snapshot on connection change