feat #486 enhancements in DomElementWrapper

1. Added support for WAI ARIA (`aria-*`) attributes in `getAttribute`
2. Added support for custom `data-*` attributes in `getAttribute`
(previously they could have been retrieved only with `getData`)
3. Added support for expandos with multiple dashes (`data-foo-bar`) in
`getData`/`getAttribute`
4. Added `setAttribute`

Close #486