Facilitate concurrent edits: Handle out of sync changes between stored and cached versions of NeoDash.

[nielsdejong]

Handling true concurrency is very complicated as it raises a variety of questions around merging edits. However, we can produce a notifcation that a local storage dashboard is out of sync with the saved version in the database. This should probably be checked at startup time, after the user connects. If we see a dashboard in the database with the same UUID but different reports we should produce a notification and ask if they want to override their local dashboard.