refs https://github.com/TryGhost/Team/issues/584
refs https://github.com/TryGhost/Team/issues/1498
- updated newsletter save routine in `edit-newsletter` modal to open an email confirmation modal if the API indicates one was sent
- modal indicates that the previously set or default email will continue to be used until verified
- response from API when saving looks like `{newsletters: [{...}], meta: {sent_email_verification: ['sender_name]}}`
- added custom newsletter serializer and updated model so that the `meta` property returned in the response when saving posts is exposed
- Ember Data only exposes meta on array-response find/query methods
- https://github.com/emberjs/data/issues/2905
- added `/settings/members-email-labs/?verifyEmail=xyz` query param handling
- opens email verification modal if param is set and instantly clears the query param to avoid problems with sticky params
- when the modal opens it makes a `PUT /newsletters/verify-email/` request with the token in the body params, on the API side this works the same as a newsletter update request returning the fully updated newsletter record which is then pushed into the store
- removed unused from/reply address code from `<Settings::MembersEmailLabs>` component and controller
- setting the values now handled per-newsletter in the edit-newsletter modal
- verifying email change is handled in the members-email-labs controller
- fixed mirage not outputting pluralized root for "singular" endpoints such as POST/PUT requests to better match our API behaviour
refs https://github.com/TryGhost/Team/issues/1441
- switched "leave settings" confirmation modal on members email settings screen over to modern modal pattern
- removed unused `showEmailDesignSettings` property and `closeEmailDesignSettings()` action on `<Settings::MembersEmailLabs>` component
- the used property and action live on the controller, looks like it was a copy/paste hangover when functionality was moved to a component
- added newsletter model
- includes design-related attributes which are not yet supported by the API but are due to be added
- includes `default` attribute but there is no setting for it, due to be removed from the API but it's needed for save not to error for now
- set up basic mirage model and endpoints
- added validation for main settings to match API validation
- added `EditNewsletter` modal
- separate tabs for general newsletter settings and design-related settings
- used for both creating and editing newsletters
- added `/settings/members-email/newsletters/new` and `/settings/members-email/newsletters/:id` routes
- both display the `EditNewsletter` modal on top of the members-email settings screen with the appropriate newsletter model
- updated `<Settings::MembersEmailLabs::NewsletterManagement>` component to work with real newsletter model instances and the new add/edit routes
- removed now-unused `newsletter` service that was providing mocked data for earlier design iteration
refs https://github.com/TryGhost/Team/issues/1441
- pulls newsletter-related functionality into one place to keep higher-level components from knowing about too many concepts and becoming bloated
- updated temporary newsletters service to have fully tracked objects so the `active/archivedNewsletters` properties can be closer to how they will work with full models
refs https://github.com/TryGhost/Team/issues/1441
- duplicated route/controller/template and component to `-labs` versions so larger changes and refactors can be made without affecting the GA code
- added redirect for `/settings/members-email -> /settings/members-email-labs` when `multipleNewsletters` flag is enabled
- cleaned up multiple-newsletters related code from the non-labs component
