refs https://github.com/TryGhost/Team/issues/1149
- added fixed width of the main menu to the tablet-size media queries so it doesn't snap back to a smaller width after animating
refs https://github.com/TryGhost/Team/issues/1149
- added `ember-css-transitions` library that provides a modifier that adds/removes classes used for animating elements in and out, automatically creating a clone for destroyed elements
- added a wrapper class around the `main` and `design` nav menu contents so they could be individually animated
- used the new `{{css-transition}}` modifier to animate the sidebar menus in/out
- ensured main menu doesn't animate on first render of the parent `<GhNavMenu>` component so there's no animation when Admin is loaded
refs https://github.com/TryGhost/Team/issues/1149
- changed `current-when` for the design settings title to only be active on the index screen which corresponds to the setting groups being active/usable
- updated styles to use the `.active` class rather than just `:focus`
- added empty archive screen
- added indication of archive offer on detail page
- set default dropdown style to non-selected
- removed archive button for new offers
refs https://github.com/TryGhost/Team/issues/1136
- adds dropdown for active/archived offers selection
- wires active/archived offers on list screen to API
- filters offers list on archived/active based on selection
no issue
- icons seemed to disappear when sections above are opened, or they lost attachment when scrolling
- added `position: relative` to the nav item container so the `position: absolute` children are correctly contained
refs https://github.com/TryGhost/Team/issues/1084
- updates shareable offer link UI to to open directly instead of route
- calculates offer url from code and updates in link modal
- wires copy button on link modal
- removes route based link code for modal
