Setting type="button" to prevent form submission

When a control is rendered inside of a form element, handlePointerUp_ does virtually nothing: preventing mousedown or/and mouseup event doesn't prevent form submission, we should listen for click and keypress or, to be more accurate, DOMActivate.

Or we can just set type to "button" (which is already used in ol.control.Zoom) and thus disable the defaullt DOMActivate logic.