The `STObject` member function `setType()` has been renamed to
applyTemplate() and modified to throw if there is a template
mismatch.
The error description in the exception is, in certain cases,
used, to better indicate why a particular transaction was
considered ill formed.
Fixes#2585.
* 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