refs https://github.com/TryGhost/Team/issues/1225
Re-using the existing pattern of creating an image card and having it launch an image selector was proving to have a lot of edge cases when we wanted a more streamlined in-line image selector for gifs.
- added a new `'selector'` type to card definitions
- requires a `selectorComponent` argument that is the name of a component that renders the media and handles search
- updated card components to open the selector component when respective menu item is activated
- updated slash menu to instantly trigger the selector component when the slash command matches a card and is followed by a space so that searches continue inside the selector
- added `<KoenigMediaSelector>` component that wraps the card-definition provided component and handles escape key, clicks outside of the editor, and provides a stripped down API to the child component for selecting/closing
- added `<KoenigMediaSelectorTenor>` which mostly replicates the `<GhTenor>` component but has different styling and uses the provided media selector API
