ngDisabled should also set aria-disabled

[marcysutton]

Because of Angular.js Material Design's use of element directives, aria-disabled must be set alongside disabled to communicate a control's state to assistive technologies. disabled is only valid on a subset of HTML elements or their prototypes (using Web Components), including input, button, select, and more. More on disabled elements: http://www.w3.org/TR/html5/disabled-elements.html

This affects material-checkbox, material-button, material-radio, material-tabs, material-slider and any component that can be disabled.

[ThomasBurleson]

@marcysutton - great issue here!

[marcysutton]

I'm actually seeing incorrect aria-disabled values when inputs are disabled:

Material-slider has disabled and aria-disabled="false", which is a mismatch. Could be related to #272.

[marcysutton]

Closed with ngAria added to project 96c0095