Add background image switch

[Elijas]

Except for pop notification for pin or unpin operation, switch backgroud with desktop can make switch more clear .

AutoAssociateBackgroundWithDesktop := false
BackgroundPicPaths := ["C:\Users\A\Pictures\VDPic\day.jpg", "C:\Users\A\Pictures\VDPic\snow.jpg", "C:\Users\A\Pictures\VDPic\sex.jpg", "C:\Users\A\Pictures\VDPic\cool.jpg"]


……

changeBackgroundWithDesktopId()
{
    global CurrentDesktop, BackgroundPicPaths, AutoAssociateBackgroundWithDesktop
    filePath := BackgroundPicPaths[CurrentDesktop]
    if (AutoAssociateBackgroundWithDesktop and filePath and FileExist(filePath)) {
        DllCall("SystemParametersInfo", UInt, 0x14, UInt, 0, Str, filePath, UInt, 1)
   }
}

_Originally posted by @fanlushuai in https://github.com/pmb6tz/windows-desktop-switcher/issues/55#issuecomment-629744607_