Window control placement

The window controls (close, minimise,maximise) are always on the right.
I have my system set to place them on the left but the App Center does not change the placement

This is because the flutter toolkit implementation for Yaru does not follow org.gnome.desktop.wm.preferences’s button-layout setting.

/cc @dloose

Yes we have an issue for this in yaru.dart

https://github.com/ubuntu/yaru.dart/issues/532

And also a pull request that needs review/rebase

https://github.com/ubuntu/yaru.dart/pull/762