webadmin,userportal: Improve UiCommon Editor integration

This patch makes UiCommonEditorVisitor work with new interface
(UiCommonEditor) instead of using WidgetWithLabelEditor class
directly.

UiCommonEditor interface can now be implemented by any specific
editor class, i.e. we're no longer limited by using only
WidgetWithLabelEditor bound to specific widget type
(AbstractValidatedWidgetWithLabel).

Change-Id: Ifd5a5456966b99e9d2eef8b5a0199f04793b315e
Signed-off-by: Vojtech Szocs <vszocs@redhat.com>