webadmin: remove using Config.DefaultConfigurationVersion

use AsyncDataProvider.getDefaultConfigurationVersion() instead

We want to update default value only in a single component;
and Config is a common class.

Change-Id: Id935d4d73f6959243723db5a416b4d253cc9b332
Signed-off-by: Gilad Chaplik <gchaplik@redhat.com>