Add Songhay.Framework.Core project and package

[BryanWilhite]

a project called Songhay.Framework.Core intends to centralize all the non-.NET-Core/Standard features the Studio intends to support:

• ObservableSortingCollection, RefreshEventArgs.cs, SortableCollectionView currently under 4.6.1
• abandon BackgroundWorkerUtility and BackgroundWorkerUtilityData
• roll-up ConfigurationManagerExtensions, DataServiceCollectionExtensions ❓, EncryptionMetadataExtensions.ConnectionStringSettings, ICommunicationObjectExtensions, RestApiMetadataExtensions.ServiceModel ❓, TraceSourcesExtensions.ConfigurationManager
• roll-up ISyndicatable
• roll-up BasicHttpBinaryBinding ❓
• roll-up FrameworkUtility.Process
• roll-up Songhay.Net.HttpWebRequest

[BryanWilhite]

building this project may not be necessary as a combination of these tools might make everything work from a .NET Standard library:

• https://docs.microsoft.com/en-us/dotnet/standard/analyzers/api-analyzer
• RuntimeInformation.IsOSPlatform() https://docs.microsoft.com/en-us/dotnet/api/system.runtime.interopservices.runtimeinformation.isosplatform?view=netframework-4.8
• <TargetFrameworks> https://weblog.west-wind.com/posts/2017/jun/22/multitargeting-and-porting-a-net-library-to-net-core-20 by @RickStrahl
• https://docs.microsoft.com/en-us/dotnet/framework/configure-apps/how-to-enable-and-disable-automatic-binding-redirection
• https://youtu.be/hLFyycJVo0I?t=1081 by @terrajobst
  

maybe not: only .NET Framework 4.72 would take full advantage of a the version .NET Standard the Studio intends to support

[BryanWilhite]

#20 should address this issue