refs https://github.com/TryGhost/Toolbox/issues/308
- we have a pattern of using plurals for endpoints but `email_preview`
was implemented without it
- in v5, we're fixing that so we need to update Admin to take that into
account
refs https://github.com/TryGhost/Team/issues/559
refs 054a5f15f5
- with the update of `ember-promise-modals` we started to get deprecation warnings when using `modals.open('modal-component-name')`
- upcoming Ember build updates will introduce tree shaking but using run-time lookup of modal components by name works against that because it's not statically analysable
- switched to importing components and passing the component class directly, eg. `modals.open(ModalComponent)`
- standardized modal component class names with a `MyModal` style to get better behaviour in code editors when it auto generates imports
- dropped the modal defaults from the modals service because we can now use a static `modalOptions` property on the modal components themselves when we want to override the defaults
refs https://github.com/TryGhost/Team/issues/559
refs https://github.com/TryGhost/Team/issues/1277
- switched modal implementation to the newer promise-modal style
- added `<GhEmailPreviewLink>` component that renders a link that when clicked opens the modal
- removes the need for templates/controllers to manually handle modal opening/closing and to pass actions down from parents
- updated all places we were triggering an email preview modal to use `<GhEmailPreviewLink>`
