webui: move RPC result extraction logic to Adapter
It enables declarative extraction of values from partial
results of a batch commands and also further extensibility
in custom adapters.
The default adapter has detection logic for this extraction so
it can use bare record or extract data from normal or batch RPC
command.
Minor change of user plugin fixed:
https://fedorahosted.org/freeipa/ticket/4355
Reviewed-By: Endi Sukma Dewata <edewata@redhat.com>