LP#1850547: eg-combobox: handle startId if idlClass is set

LP#1850547: eg-combobox: handle startId if idlClass is set

This patch teaches the Angular eg-combobox component to retrieve
the record indicated by the startId attribute when an IDL class
is specified.

Sponsored-by: Evergreen Community Development Initiative
Sponsored-by: Georgia Public Library Service
Sponsored-by: Indiana State Library
Sponsored-by: C/W MARS
Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>
Signed-off-by: Tiffany Little <tlittle@georgialibraries.org>
Signed-off-by: Bill Erickson <berickxx@gmail.com>