feat(Button): Prevent click on disabled button

[jeffcarbs]

Fixes #929

• Prevent clicks on a disabled button (both mouse clicks and "clicks" via focus + pressing enter). Also called preventDefault on the click event when the button is disabled to prevent form submission (if within a form) or link following (if an a).
• Pass back props to the onClick and documented the onClick prop as spec'd in RFC: all event handlers should callback with (event, data) #623 (comment)

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[levithomason]

Looks good, thanks!