Moves in-process to UseIISIntegration, removes Server.IIS namespace (#443)

IISIntegration.sln

samples/NativeIISSample/NativeIISSample.csproj

samples/NativeIISSample/Startup.cs

samples/NativeIISSample/applicationhost.config

...NetCore.Server.IIS/Microsoft.AspNetCore.Server.IIS.csproj

src/Microsoft.AspNetCore.Server.IIS/NativeMethods.cs

...gration/Microsoft.AspNetCore.Server.IISIntegration.csproj

...crosoft.AspNetCore.Server.IISIntegration/NativeMethods.cs

...t.AspNetCore.Server.IISIntegration/Server/DuplexStream.cs

...r.IISIntegration/Server/HttpProtocol.FeatureCollection.cs

...ore.Server.IISIntegration/Server/HttpProtocol.Features.cs

...t.AspNetCore.Server.IISIntegration/Server/HttpProtocol.cs

...t.AspNetCore.Server.IISIntegration/Server/IISAwaitable.cs

...NetCore.Server.IISIntegration/Server/IISHttpContextOfT.cs

...etCore.Server.IISIntegration/Server/IISHttpRequestBody.cs

...tCore.Server.IISIntegration/Server/IISHttpResponseBody.cs

....AspNetCore.Server.IISIntegration/Server/IISHttpServer.cs

...AspNetCore.Server.IISIntegration/Server/OutputProducer.cs

...Core.Server.IISIntegration/WebHostBuilderIISExtensions.cs

...ionalTests/IISIntegration.IISServerFunctionalTests.csproj