fix #355 button widget not focusable

In IE8+ the Button widget is not focusable because of the onfocusin method
used as an hack in <IE8
Closes #357
fix #365 skin inherited by the Bridge

closes #368
fix #273 additional whitelisted attributes

autofocus, autocomplete, autocapitalize, autocorrect and spellcheck attributes are now in the whitelist.
closes #372
doc Getting started with AT