deprecation notice to plugin compatibility shims
- When qml-common became a thing, we left qs.Widgets shims in place for
plugin compatibility
- It's annoying to need to maintain them when qml-common has any change,
add a warning so we can safely deprecate them in the future
- One shot rename the common stuff to D to make it shorter and nicer to
write
- Introduce multi-account greeter login with per-user theme previews
- Add `dms greeter sync --profile` for secondary users with or without sudo
- Add Manage greeter group membership from Settings UI → Users Tab