AutoGenerateBindingRedirects doesn't work properly

When an addin's csproj has both the `AutoGenerateBindingRedirects` and `GenerateBindingRedirectsOutputType` properties defined to `true`, the `App.config` file is (potentially) enriched with needed bindingRedirects when it is copied as `MyAddIn.dll.config`.

However, within the `CreateExcelAddIn` task, the [handling of `App.config`](https://github.com/Excel-DNA/ExcelDna/blob/master/Source/ExcelDna.AddIn.Tasks/CreateExcelAddIn.cs#L198) uses the original `App.config`, and therefore misses the bindingRedirects.

As a workaround, one can add to the csproj a target along the lines of :
```








```
But it would probably be better to try to use the processed `MyAddIn.dll.config` file in the task.