ref(SimpleWebSource): Fix Release Entry source to work with parameter url

[johanneswanzek]

When using a Storage URL with parameters (e.g. Azure Blob Storage) getting the release file (/RELEASES) works perfetly. Unfortunatly the downloading of the package doesnt work because it discards all query parameters while building the URI.
Using the same mechanism as GetReleaseFeed by utilizing the Utility.AppendPathToUri makes it work perfectly with parameterized Urls.

[caesay]

I suspect this will break when an absolute path is provided for a release package. For example:

If sourceBaseUri is https://my.domain/packages and releaseUri is MyPackage-1.0.0.nupkg, then source should be https://my.domain/packages/MyPackage-1.0.0.nupkg. This should work fine.

If sourceBaseUri is https://my.domain/packages and releaseUri is https://my.packages.domain/MyPackage-1.0.0.nupkg, then source should be https://my.packages.domain/MyPackage-1.0.0.nupkg. I suspect this will not work properly after this PR.

Could you add a unit test to cover both of these possibilities and check to see if the latter case works with your change?