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
- rework the way social links are displayed/editted; we now only allow to
enter a so called "handle" and then substitute that in the final URL
template
- move the "icon" model role to NIM backend
This has several advantages:
- we display only the "handle" and don't have to elide some long URL
- we won't let users enter random URLs into their profile and spoof the
viewing part into clicking it
Additionally, make the social link "button" clickable -> navigate to the
target URL, and make the tooltip behave as "usual" (on mouse hover).