* Use version overrides for ImageSharp 2
* Move Directory.Packages.props to root, use GlobalPackageReference and replace Microsoft.CSharp with Microsoft.CodeAnalysis.CSharp
* Replace NPoco.SqlServer with NPoco and remove unused System dependencies
* Fix package validation and MSBuild warnings
* Add nuget.config and enable package source mapping
* Remove explicitly set C# language version
* Add empty Directory.Packages.props file for acceptance test
* Downgrade SixLabors.ImageSharp back to 3.0.2 because of breaking changes
* Update ImageSharp/ImageSharp.Web to 3.1.0 and use ComputeHMAC