refs https://github.com/TryGhost/Team/issues/1210
- when rendered, show button as greyed out if either text or url is missing
- show "Add button URL" in tooltip if the url is missing
- show "Add button text" in button if the text is missing
- adds wrapper element so the tooltip is not greyed out
no issue
The logic for "delete if empty" was duplicated in two places:
1. when `createComponentCard` is used to register a card, this option method was used when cleaning up a post when first rendering (cards in empty state can be saved before the editor auto-removes them but we don't want to show them again)
2. inside of card's own delete-if-empty handling on certain actions such as deselection or leaving edit mode
- added an `ifEmpty` property to each card component
- used by the editor's first-render cleanup routing if the property is present
- can be re-used internally for the card's own deselect/exit-edit-mode behaviour
- updated the cleanup routine in `<KoenigEditor>`
- added a `allComponentCardsRegistered` property that will return `true` when the `.component` property is set on every card (the property is set during card component initialisation so we're at the mercy of Ember's render process so not all card components will be immediately registered)
- swapped `_cleanup` for `_cleanupTask` that will wait for `allComponentCardsRegistered` to be `true` before performing cleanup, ensuring that we always have access to the card component's `isEmpty` property even when Ember renders cards across multiple render batches
- checks for `isEmpty` being a boolean and will delete the card if it's value is `true`
- updated all cards that had delete-if-empty behaviour
- added `isEmpty` properties
- removed duplicated logic in the `createComponentCard` calls
