Update for ASP.NET Core 2.x patterns

[poke]

Some minor adjustments to make this starter template more in-line with the current practices, and to fix double logging output.

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In ASP.NET Core 2, configuration moved up to the web host builder, so the Startup class should not create its own configuration builder but just have the existing configuration injected.

Similarly, logging also moved up and is part of the default web host builder. Registering providers on the logger factory again will just cause the logging messages to be duplicated (e.g. there were two parallel console loggers before).

• Use CreateWebHostBuilder pattern found in ASP.NET Core 2.1.
• Add default appsettings.json and appsettings.Development.json.

[MarkPieszak]

This is great great job @poke !! 🍾

I should of figured we have some older ways of doing aspnet core stuff here! You rock 🎸