Adapt PackageServiceStreamProvider to add additional route data when con...

Hi,

thanks for the work on this nuget server. I'm using it to host several repositories in one web application.

I use a modified version of the route mapper with additional placeholders.

The chang I did searches for additional route data in the current service request which are also needed to construct the URL for the package download.

Would be nice to see this merged.

Kind regards
Daniel