WIP: Display settings improvements
The first commit is pretty straightforward, just the center dialog on monitor where cursor is whenever
xfce4-display-settings --minimal is invoked (usually via global shortcut). This is useful when this dialog ends up out of screen.
The second commit adds the behavior found in Windows and Gnome to quickly switch between available presets whenever
xfce4-display-settings --minimal is invoked and it's already open. Unfortunately the dialog is not correctly centered anymore because the calculation takes into accounts monitors configuration before presets are applied.