Controlled component

Is there a way to set the 'open' element by key as a prop, so Grid can be used as a controlled, stateless component? You could use this to, say, synchronise the open state with a router system.

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Start at the Grid component and trace how its open element is currently stored and changed; compare that flow with the proposed openKey prop. Done means Grid can receive the open key as a prop and remain controlled and stateless, including the router-synchronization use case.

Written by the indexing model from the issue text.