Add detection if user is actively using PC

[lemedege]

Set user active or idle based on last input on keyboard.
Make timeout customizable, and possible to disable completely by the user

http://joelabrahamsson.com/detecting-mouse-and-keyboard-input-with-net/

[DllImport("User32.dll")]
private static extern bool GetLastInputInfo(ref LASTINPUTINFO plii);

[StructLayout(LayoutKind.Sequential)]
internal struct LASTINPUTINFO
{
    public uint cbSize;
    public uint dwTime;
}