Support iOS Safari browsers clicking to dismiss modal

iOS browsers will only generate a click event when a particular DOM element has a specific binding to it or if it has `cursor: pointer` styling applied to it.

Ember's `.on('click')` is not sufficient for iOS' browsers, so using the `onclick` attribute on the modal DOM element is used.

The contents is a noop, but it will still cause iOS browsers to generate a click event, to which `closeOnClick` will respond to.