* Adds notification icon circles and associated storybook stories
* Fix image paths in circle-icon.stories and message-circle-icon.component
* Code improvements for icon circles PR: remove additional z-index, make iconSource required
* Use component story format in circle-icon.stories and message-circle-icon.stories
* Remove success and info circle icons, as not presently needed
* Rename message-circle-icon to alert-circle-icon
* Small code fix ups for alert-circle-icons
