LP1831785 Combobox pcrud selector and pkey support

LP1831785 Combobox pcrud selector and pkey support

Teach the PCRUD-driven combobox to use the IDL class' selector field
as the sort and display field when no idlField value is provided.

Teach the async source to use the pkey field of the IDL class instead of
assuming the 'id' field.

Tweak the sandbox example to fetch data for a class which uses a
selector not called "name" and a pkey not called "id".

Signed-off-by: Bill Erickson <berickxx@gmail.com>
Signed-off-by: Jane Sandberg <sandbej@linnbenton.edu>