refs https://github.com/TryGhost/Admin/pull/2209
- `miragejs` has been extracted to a framework-independent library, the re-exports of `miragejs` elements in `ember-cli-mirage` have been deprecated making our test logs very noisy
- added `miragejs` as a top-level dependency
- updated all relevant imports to pull from `miragejs` instead of `ember-cli-mirage`
requires https://github.com/TryGhost/Ghost/pull/9426
- fixed default token component display in {{gh-token-input}}
- if no `tokenComponent` is passed to `{{gh-token-input}}` then it should default to the ember-drag-drop `draggable-object` component but instead it didn't output anything
- put `draggable-object` in quotes because `{{component}}` needs a component name rather than an object
- rename `option` attribute to `content` to match the default `{{draggable-object}}` interface
- add embedded `authors` attr to the Post model
- ensure authors is populated when starting new post
- add validation for empty authors list
- swap author dropdown for a token input in PSM
- show all post authors in posts list
- update tests for `authors`
- always provide through an authors array
- fix mirage serialisation for paginated responses (embedded records were not being serialised)
- unify tags and author inputs design
- remove highlight of primary tags
- highlight internal tags
- remove unnecessary/redundant title attributes on tags
- use SVG icon for "remove option" button in token inputs
