when switching to POST, ViewQueryRequest doesn't account for urlencoding of keys

The java-client passes urlencoded params to the core (for keys notably).
When the core switches to POST because of the size of the request, keys are not decoded (and the encoding could potentially be unknown), resulting in bad JSON and a server-side error.

The keys should be passed separately and unencoded in the ViewQueryRequest, as a JSON array String, and encoded as needed by the core.