refs https://github.com/TryGhost/Ghost/issues/9311
- adds an overlay element to the embed card so that clicks do not interact with any embedded iframes so that you can lazy click to enter edit mode
refs https://github.com/TryGhost/Ghost/issues/9311
- wraps embed card in same container as the markdown card to handle mouse selection/edit toggles etc
- add render mode to embed card
- autofocus CodeMirror editor when switching to edit mode
- fix incorrect pointer on cards
refs https://github.com/TryGhost/Ghost/issues/9311
- add a basic HTML card that renders a CodeMirror editor
- adjust styles so that CodeMirror styles for the markdown editor don't affect CodeMirror instances inside Koenig
