Added `withKeyCode` option to action helper

For actions that are fired on `keyUp`, `keyDown` or `keyPress` an option called `withKeyCode` is now available to use. It ensures that the action is called only when the given `withKeyCode` value matches the keyCode on the event.

For example:

    <input type='text' {{action 'show' on='keyUp' withKeyCode='13'}}>

This action will only fire if the event is a `keyup` and the `keyCode` is 13.
Merge pull request #5000 from crismali/enter-action-key

Added `withKeyCode` option to action helper