Integrate PR 26 to add settings for styling alerts

PR 26 gave us a settings page and styles for alert notifications.

Since beginning work on issue ~~#570~~ this is more relevant as alert boxes will now display in the course page area as well as the upper header.

It is more likely users will want / need to style them now they are being used more pervasively within the theme and it mades sense to integrate this now ahead of finishing ~~#570~~