refs https://github.com/TryGhost/Team/issues/1225
- iterations of earlier approaches (modal-image-selector, and kg-media-selector) for the gif selector were kept around whilst we narrowed down the interaction patterns, we've settled on the inline-image-selector pattern introduced in 3f3b66b668 meaning the others are no longer needed
refs https://github.com/TryGhost/Team/issues/1225
- the `imageSelector` options in the image card have been expanded to have both a `component` and a `type` property. If the `type` is set to "placeholder" the related image selector component will be rendered in place of the default upload placeholder
- updated `isEmpty()` so the card is always cleaned up if no src has been selected - prevents image selectors popping up when opening a post if it was saved whilst the image selector was open
- updated close-selector behaviour to exit back to a blank paragraph so a different image embed type can be selected easily instead of leaving an image card that you then have to delete, create a new paragraph, and choose the embed type
- added `koenig-image-card/selector-tenor` child component
- the same as `koenig-media-selector-tenor` except with the "Escape" key handling added
- added as a separate component for now to allow for easy switching until we're settled on the selector type we want
