Updating PDF-XChange Viewer

Hi calwell,
thank you for your Chocolatey packages. This is a pull request to update pdfxchangeviewer. I also changed the icon. The old icon was too detailed and is therefore not very suitable for the Chocolatey Gallery at 128 × 128 pixels. I think it’s always a good idea to take exactly the same icon which the program uses as start menu/desktop icon.