Changes to “Leaving the registry”

+ ClaimNodeRegistration (type 770) lets whoever holds the node key claim the stake to an account they control. It exists for an owner who has lost access to the owner account, and it carries a proof of ownership signed by the node key. The owner's own claim takes effect at once. Anyone else's claim is announced and executes 40,320 blocks later, unless the owner removes the node first ([[node-keys]]). An owner who has lost the owner key claims from another account, so its claim also executes 40,320 blocks later.