Use PackageReference instead of .nuspec file

[vany0114]

We need to update the project file to include all the metadata that we have into the .nuspec file, in order to remove the duplication with the releases notes, that way we only need to update the ChangeLog.md for new releases. Probably, we need to update the build.cake file.

https://docs.microsoft.com/en-us/nuget/reference/msbuild-targets#pack-target