Feature: prop for passing function when close button is clicked

[CalvinJamesHeath]

Do you want to request a feature or report a bug?
Feature
What is the current behavior?
The current behaviour is that I have to create a new button so I can pass an onClick listener, but the one by default its fine.

Would be nice to add a new prop like:

onButtonClose	function	Called when the notification close button is clicked.

[sbsangu]

Hello,

I've linked the pull request to address the feature request. It would be really helpful if someone could take a moment to review the proposed changes. Your feedback would be greatly appreciated!