Create link_appstore_downloads.sh

This script can be used to capture downloaded package files from the Mac App Store so the apps can be redistributed.
The package files will retain their Apple developer certificates but will NOT include the _MASReceipt from the App Store.
These redistributable packages are ideal for use with Casper but it does mean subsequent updates will similarly have
to be downloaded and distributed. Obviously this defeats the design of the App Store model, and should only be used with
legally purchased or free apps. Use at your own risk.