Make it easier to run tusdotnet on ASP.NET Core on .NET Framework

[smatsson]

Side note: Microsoft suck at naming stuff :)

tusdotnet runs just fine on ASP.NET Core on both .NET Framework and .NET Core (the actual runtimes). The problem is that since we use build targets to expose the correct middleware (as there is no other viable way of knowing what pipeline we run) users who run ASP.NET Core on .NET Framework need to setup an extra OWIN pipeline to be able to run tusdotnet. This is bad in terms of performance while also introducing a high threshold to run tusdotnet.

Read more: https://github.com/tusdotnet/tusdotnet/wiki/Troubleshoot:-"'IApplicationBuilder'-does-not-contain-a-definition-for-'UseTus'"-in-ASP.NET-Core

We should expose the ASP.NET Core middleware even if the build target is net452. Pros:

• No need to setup an extra OWIN pipeline to get started. Just use app.UseTus(...) and it is done.

Cons:

• OWIN and ASP.NET Core middlewares would both be exposed meaning that OWIN users would also need to install Microsoft.AspNetCore.Http.Abstractions and ASP.NET Core users would need to install Owin and Microsoft.Owin. This only applies if running on .NET Framework. For .NET Core there would be no difference.

[smatsson]

Fixed and includes new sites for testing Owin on .NET Framework, ASP.NET Core 1.1 on .NET Core and ASP.NET Core 2.0 on .NET Framework