Pass classname and id to notification component

[sradevski]

This is useful when you want to override the styling of the notification containers using something like styled-components without relying on .css files. For example, if you pass the className, you can do the following:

const StyledContainer = styled(ReactNotification)`
    .react-notification-root .notification-item {
        box-shadow: none;
    }
`

but styled-components rely on the component passing the classname to the underlying tag.

[teodosii]

Commented in the PR, closing the issue