fix #1063 section attributes binding improvement

This commit introduces the following fixes:
- when section attributes are bound to the data model, changes in `dataset` and `classList` are now taken into account
- the binding can now be recursive or non-recursive
- when the className of the section container is changed via the section wrapper classList, the data model is correctly updated.

It also removes method `aria.templates.SectionWrapper.setClassName` which has been removed from class `aria.templates.DomElementWrapper`, so thet it did not actually work.

Close #1081