Extension of callout states and minor refactoring

[DJMyles]

Note: Since devel changed so much I reforked and started again since my changes were pretty minor. I closed my old pull request and created this one.

Description

The UI kit at the moment includes a base callout class and a warning variant. This branch seeks to include states for success, error and info, updates the warning variant to use the correct $colour-warning variable and adds a small amount of refactoring by pushing some duplicated attributes to the base callout where possible.

Additional information

N/A

Definition of Done

• [ ] Content/documentation reviewed by Julian or someone in the Content Team
• [ ] UX reviewed by Gary or someone the Design team
• [x] Code reviewed by one of the core developers
• [ ] Acceptance Testing
  • [x] Cross-browser tested against standard browser matrix
  • [ ] Tested on multiple devices (TBD)
  • [x] HTML5 validation (CircleCI)
  • [x] Accessibility testing & WCAG2 compliance (npm test)
• [x] Stakeholder/PO review
• [ ] CHANGELOG updated

[klepas]

Things I need to do to get this merged:

• create a new issue for Jools in the design guide repo to document the callouts (they’ve gone missing!), adapting content from here, and from the old docs on callouts.
• ensure we have colours for all of these and that they make sense
• see if we want to extend the callout work in any way to match what the federated design clinic have been prototyping

[DJMyles]

@klepas in regards to the colours, I took the variables I used directly from the warning variables here: http://guides.service.gov.au/design-guide/foundations/colours/index.html

[klepas]

@DJMyles Re. colours: cheers. This reminds me further that we need to extend those out further, and improve the documentation on the functional vars we have (rather than just the mere descriptive colour variables) on the new documentation page…

I’m going to merge this into `develop, and then add on top of it.

There’ll be a separate ticket going into the design guide repo to update the documentation for this feature (actually, callouts got sadly lost in the transition and are missing entirely at the moment) before we do another release.