Allow passing of alert id into configObj

[timmygee]

Currently you cannot use your own alertIds when creating a notification. This is problematic if you have a react component as the message to be displayed and you want it to be dismissible by a close handle. There is no way to know the alertId at the component level because it is not passed in and the only way to dismiss the notification would be via the closeAll() method which is not ideal if there's more than one notification displayed.

This PR allows id to be passed in via the configObj and falls back to normal behaviour if it's not present.

My solution will be to pass in an id generated by sAlertTools.randomId() and should be the recommended way. I have imported it into my code via. You may wish to provide a better interface.

import sAlertTools from 'react-s-alert/dist/s-alert-parts/s-alert-tools';