[#1905] Fixed a11y issue with narration of checkboxes.

[tonyanziano]

#1905

===

Made minor changes to the <Checkbox /> component DOM structure.

The previous structure wrapped the <input> in a <label> element, and also attached an aria-label attribute to the input. This caused screen readers to narrate both the aria-label and the text within the label element.

I have changed the outer element to be a <div> with a role or "presentation" so that the screen reader ignores it, and I've wrapped the inner label text in a <label> tag so that the component follows the standard semantic structure of a labelled checkbox input. I've also removed the aria-label attribute from the <input> element, because the screen reader should know that the <label> tag describes the <input>.

I've tested this on both Windows, and Mac, and they read correctly.

Before:

After:

[coveralls]

Coverage increased (+0.009%) to 68.67% when pulling 105720d on toanzian/acc-#1905 into 87af526 on master.