Code review comment for lp:~unity-team/unity/remove-background

When we would spread the windows for the window-picker (clicking on the ubuntu icon), we'd hide all the windows and this would be our background. This branch removes that in favour of just using the normal desktop window to provide the background (either g-s-d or nautilus). We don't remove it from Unity as the binary target `unity` still uses it.

And yeah, using Unity.Testing should be removed and then feel free to commit as it works fine.