no issue
- Ember will not output the application template wrapper div in the future but it's possible to optionally enable that feature now
- fixes test harness render so that all elements are constrained to the application wrapper rather than breaking out with `position: fixed` and covering the test results
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
