Dotnet 3.0 (#20)

* .NET Core 3.0 support

* Updated .NET Core 2.2 project references
   + Updated .NET Core 2.2 Dockerfile to reference latest MS images
   + Migrated Quick Starts to individual projects
   + Moved shared test code to shared folder for reducing duplications

* .NET Core 2.2 quickstart update for JSON reference

* Travis updates Updating to xenial; dotnet sdk 3.0 install

* CHANGELOG Updates
43 files changed