closes https://github.com/TryGhost/Team/issues/1483
- updated newsletters list to use `<SortableObjects>` and `<DraggableObject>`
- swapped the `filteredNewsletters` reactive getter for a tracked property because `<SortableObjects>` replaces the value with a new array when re-ordering which isn't compatible with a getter
- required explicit update of the list any time the list should change through filter swap, archive, unarchive
- required explicit update of the list via router event when leaving the "new newsletter" route so any newly added newsletter can be displayed
- added action for handling update of `sort_order` properties when a re-order occurs
- updates every newsletter setting `sort_order` of the active newsletters first based on the new order, followed by all archived newsletters following their existing order
- disabled sorting of newsletters in the archived newsletters list
- hides the grab handle and disables the resize on hover
- allowing re-order of archived newsletters would complicate the re-order+save algorithm and re-ordering archived newsletters doesn't have a use-case
closes https://github.com/TryGhost/Team/issues/1476
- added dropdown for switching between active and archived newsletters
- modified the "default" newsletter display so it's only activated when a single active newsletter is shown
- added ability to un-archive a newsletter with a switch between "archive" and "un-archive" actions based on newsletter status
- if all archived newsletters are un-archived, automatically switches to "active" filter so you're not left with an empty list
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
