adding interactivity to answer reveal

- non-js shows question and answer with no trigger
- trigger uses dough collapse to reveal answer
- transitions on plus icon to convert to minus when open
- overridden styles for call out to MAS green
- todo: decide whether callout needs to be tight
  with hide answer 'bar' as per design or can be left
  as it is now
We should probably move these to semantic names i.e. $inline-callout-link-color and nest them in the local _settings.scss file as discussed on Tuesday.

Couple of instances of this in this file.