[DesktopView] show() ConfigView when it is already opened

requestActivate() doesn't raise the window. The same had been done in PanelView but not
for DesktopView. This way a minimized config dialog (e.g. you want look at the wallpaper
in its full glory) will be raised if you open it again through the applet/desktop context menu.

CHANGELOG: A minimized config dialog on the desktop (e.g. wallpaper settings) will now be un-minimized when trying to open it multiple times

Reviewed-By: David Edmundson