Add custom class when creating a notification

Hi, I want to display a notification with a short sentence and an in-line button in some cases and need to add a conditional class into the notification somehow as I also want to keep the non-inline version.

This could be also nice for implementing custom-level notifications that some advance users might want to make.

Thanks for the sugestion @hakunin. I'm running out of time lately, so I'll keep this labeled as an enhancement.