refs https://github.com/TryGhost/Team/issues/1206
- This only solves partially the line-returns being eaten by the editor. When editing a card with a line return, it will be removed.
refs https://github.com/TryGhost/Team/issues/1206
- prevents text in curly brakets from being wrapped into a <code> tag
- updated the callout card to this generic textarea editor instead of the email-specific editor
refs https://github.com/TryGhost/Team/issues/1209
- adds new `KoenigHtmlTextarea` component for entering multi line html in cards
- updates accordion card to use html text area component