Button Re-write

This replaces PR #1216 

This includes new widget controlgroup which replaces buttonset
Current known issues 
 - [x] Checkboxradio testfailure missing default element (@scott_gonzalez said it should not have one because it cant be sane ) this causes common tests to fail
 - [ ] Backcompat
 - [x] Controlgroup icon only buttons 1px too short in chrome, firefox extra weird @jaspermdegroot think you could take a look?
 - [x] demos/controlgroup/default.html As above, labels should demo something
 - [x] demos/checkboxradio/default.html doesn't have the "command line" anymore, but still doesn't look like a demo. Labels should reflect some real world usecase.
 - [ ] demos/button/icons.html still looks like a visual test, not a demo

[ARIA says](http://www.w3.org/TR/wai-aria/roles#toolbar): "Authors MUST supply an aria-label property on each toolbar when the application contains more than one toolbar." - how do we deal with that? Just mention it in our documentation for controlgroup? Or is it something we should enforce in the widget?

I've looked for a reference ARIA toolbar implementation. There's an [example](http://www.w3.org/TR/wai-aria-practices/#accessiblewidget) in WAI-ARIA 1.0 Authoring Practices, which sets `tabindex="0"` on the toolbar. Though the example also uses inline event handlers and image elements for buttons, so it doesn't look like a good reference.

[This example](http://test.cita.illinois.edu/aria/toolbar/toolbar1.php) doesn't use tab index, but allows cursor navigation of the buttons with the toolbar.

May need some more research.