Add support for change event

[dillingham]

Request for change event support. Would allow future support other packages

If that package were able to select the unique field as proposed,
Would enable to do the check when it changes the text of the unique field.

tomhatzer/nova-slug-field#2

Populating this text field dynamically would not trigger a keyup or blur event.
Therefore wont check unique.

Would be a perfect combination with your package for immediate unique urls :)