@redmunds and @peterflynn 
We can't use jQuery `on` handler here since we have some DOM elements that have default actions. ie. links in Quick Doc that takes action on enter keys. With this change, you can no longer tab to any link in Quick Doc. 

With `on` handlers, the keydown events are called on bubbling phase (event.phase == 3) . So it is too late if the DOM element that has focus also has a default action which is handled in event.phase == 2. So we need to revert to the original keydown hook which is handled in capturing phase (event.phase == 1).