no issue
- add eslint-plugin-ember, configure no-old-shims rule
- run `eslint --fix` on `app`, `lib`, `mirage`, and `tests` to move imports to the new module imports
- further cleanup of Ember globals usage
- remove event-dispatcher initializer now that `canDispatchToEventManager` is deprecated
closes https://github.com/TryGhost/Ghost/issues/8611
- fix positioning of "static page" throbber
- fix PSM throbbers re-appearing after PSM close/open (need to use `pushObject` instead of `push` so that it's KVO compliant and the `_activeThrobbers` CP is updated)
- fix order of `willDestroyElement` so that we don't attempt to use `get` after the component is destroyed
- fix issue in Chrome that was preventing the Meta Data link from sliding the PSM panels
refs https://github.com/TryGhost/Ghost/issues/5168
- adds a `tour` service that handles syncing and management of tour throbbers & content
- adds a `gh-tour-item` component that handles the display of a throbber and it's associated popover when clicked
- uses settings API endpoint to populate viewed tour items on app boot/signin
- adds `liquid-tether@2.0.3` dependency for attaching throbbers and popups
- adds initial tour contents
