Fix checkbox click for checkboxes without a label.

[arkwright]

Unfortunately #407 broke checkboxes without labels — they aren't clickable using a mouse. This fixes that.

Currently the <input> is rendered offscreen, a <div> is used visually in its place, and a <label> is overlayed on top of the <div> to receive mouse clicks.

This PR brings the <input> back onscreen and visually it using opacity:0. I also added cursor:pointer for consistency with the <label>. I should note that some consider this to be a usability antipattern.

[cchaos]

Technically, #407 didn't break this functionality ;) It was always like this and you are able to add the propinList to be sure that it displayed without a label.

Perhaps we just need to change that prop name, or add an alias to the prop name, that says noLabel and appends that class.

[cchaos]

And we should probably add the same ability to the radio buttons as well.

[arkwright]

Ah, thanks! I see what's going on now. Upgrading from 0.0.21 to 0.0.22 (which contains #407) did break our code, but that's because we weren't passing type="inList". When I add that type, everything works.

I'll open another issue for the semantic discussion.