WebUI: Possibility to choose object when API call returns list of objects
In case that API call returns array of objects which contains data, using
'object_index' attribute in adapter specification we can set which object
should be used.
It is possible to choose only one object specified by its index in array.
Part of: https://pagure.io/freeipa/issue/6601
Reviewed-By: Petr Vobornik <pvoborni@redhat.com>