* Rename isArray to isArrayOrNull
* Rename isObject to isObjectOrNull
* Introduce isArray and isObject
* Change as many uses of isArrayorNull to isArray as possible
* Change as many uses of isObjectorNull to isObject as possible
* Reject null JSON arrays for subscribe and unsubscribe
Check and modify amendment blocked status with each new ledger (provided
by @wilsonianb). Honor blocked status in certain RPC commands and when
deciding whether to propose/validate.
Fixes: RIPD-1479
Fixes: RIPD-1447
Release Notes
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This resolves an issue whereby an amendment blocked server would still
serve some RPC requests that are unreliable in blocked state and would
continue to publish validations.