- get rid of the `amISectionAdmin` for good (was done only partially in
82a1ed2f7aa46750fb5ab891e2ce40f61287eccb)
- fix the corresponding storybook pages
Fixes#10963
Implement the UI part of Profile/Settings/Showcase:
- Communities/Accounts/Collectibles/Assets tabs
- drag and drop of items between "hidden" and "in showcase" sections
- ability to set individual items' visibility
- persistency (showcase saved across restarts), not exposed yet due to
missing backend API
Closes#9936