State in Metabase can become stale if tables are removed

[pdobacz]

If I import a table, define a question/SQL/dashboard query based on it, and then delete, the state in Metabase will be incorrect and throw errors (understandably). What's worse, the errors don't provide useful info about what's wrong, just ⚠️ "There was a problem displaying this chart."

We may consider introducing some assistance when removing a table with a Metabase state attached to. We might like to have a dialog open up on remove, explaining what's happening and asking the user what should be done (drop the related Metabase objects, or keep them, anticipating the user importing a table with the same name).