LP#1850547: eg-combobox: set a limit on number of entries fetched for idlClass

LP#1850547: eg-combobox: set a limit on number of entries fetched for idlClass

The automatically-created data source for eg-combobox when used
in idlClass will now limit itself to 100 entries in order to avoid
scenarios where it attempts to fetch all patrons in the database
or the like.

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>