DNM: Defect fix: MAGN-1380 - Add tests for files from the future

Add tests for files from the future
This is most probably my fault, these magic numbers should not really be left in the source codes. Could you please add an enumeration for them? I think it can be made under ```Nodes.Utilities``` namespace like so:

```cs
enum ButtonId
{
    Cancel = 43420,
    DownloadLatest,
    Proceed,
    // Add others which make use of TaskDialog 
    // here and give them appropriate names
}
```

Please also update all other uses of task dialog (see if anyone else uses ```TaskDialogEventArgs``` in other files and update them as well. The magic numbers should never have made it into the repository, sorry!