Turn extension-prefs into an app
GNOME Software's extension support isn't great, and better off in a specialized app. The plan is to turn
gnome-shell-extension-prefs into this app.
This is the first part of implementing the corresponding mockup, and deals with "appifying" the tool.
Follow-up merge requests will change the row appearance and add support for deinstallation and updates.
Related: #1968 (closed)