Touch target size should be bigger

[jouni]

Currently, it’s not very easy to hit the touch target of paper-radio-button on a touch device (at least on iOS). You need to hit exactly inside the root element boundaries (which includes the label) to toggle the state.

For native input elements, iOS extends the touch target area outside the visible parts of the element (not sure about Android), making it easier to hit it. This doesn’t apply for paper-radio-button.

(Copied the from the same issue in paper-checkbox)

[bicknellr]

(comment + workaround on PolymerElements/paper-checkbox#123)