refs https://github.com/TryGhost/Ghost/issues/9311
- add `{{koenig-card-markdown}}` component that renders an auto expanding textarea with the markdown card value
- add `{{card-markdown}}` that is an alias of `{{koenig-card-markdown}}` for backwards compatibility - all of our pre-1.0 alpha cards and our current markdown implementation do not have the `koenig-` prefix in their card names
refs https://github.com/TryGhost/Ghost/issues/9311
- adds the `koenig-card-image` card that renders an `<img>` element
- adds text expansion to convert markdown images into the new image card
refs https://github.com/TryGhost/Ghost/issues/9311
- use a similar approach as used in `ember-mobiledoc-editor` to render a div into the editor canvas then use Ember's `{{-in-element}}` helper as a wormhole to render an ember component card into the new div
- adds a `createComponentCard` util for setting up the necessary rendering boilerplate for Ember component cards