Renamed to on_disabled_update.
Also passed in the new state of disabled. It's more convenient this way,
than having the subclasses call disabled_get.
Also simplify some code...
Ref T5363
Also prefix with widget.
I want to rename this as child rather than sub. It's inconsistent with
the other parent/child hierarchies. Anyway the various hierarchies are
confusing, so let's keep this name :)
Ref T5363
Some names have not been changed, hopefully making a distinction
between legacy APIs and internal code (elm_layout_blah) and valid EO
usages.
This means many internal functions are still elm_layout_ as their
sole purpose is to support the legacy API.
Ref T5315
Marcel Hollerbach
Jean-Philippe Andre