[dialog addon] Add more options

* closeOnEnter: whether or not the dialog should be closed when you
  press enter with it focused. Defaults to true.

* closeOnBlur: whether or not the dialog should be closed when the
  textfield or button loses focus. Defaults to true.

* onClose: a callback that will be called when the close function
  completes.

* onInput: very similar to onKeyDown, but uses the input event instead
  of keydown. Just an additional event handler basically.
[dialog addon] Small style tweaks

Issue #2777