refs https://github.com/TryGhost/Ghost/issues/9311
- initial CSS for container card outline, selection state, toolbar, etc
- adds `{{#koenig-card}}` component to be used inside of component card templates to handle the default card container HTML, mouse interactions, etc
- update `{{koenig-card-markdown}}` to use the new `{{koenig-card}}` component
- add render/edit mode views
- focus the textarea when entering edit mode
- updated `{{koenig-editor}}`
- add <kbd>Cmd+Enter</kbd> command to put a selected card into edit mode
- when inserting new cards put them into edit mode immediately
- move edit/select methods out of actions and into normal methods so that timing is easier to reason about
- skip `cursorDidChange` process when cursor changes as a result of a card selection, fixes issues with `selectCard` being triggered multiple times unexpectedly
