Make our self host depend on owin self host package

[davidfowl]

There's a new package Microsoft.Owin.SelfHost that we should take a dependency on in our self host package.

[Xiaohongt]

With Owin release branch, when install or update Owin self host package, it will auto update existing Startup to below, and when uninstall Owin self host package, it will remove the Startup.
I will verify on Owin dev branch.

    public class Startup
    {
        public void Configuration(IAppBuilder app)
        {
#if DEBUG
            app.UseErrorPage();
#endif
            app.UseWelcomePage("/");
        }
    }

[Xiaohongt]

same behavior on Owin dev branch

[davidfowl]

Nice, I think we should make them remove the Startup.cs from the package.

[Xiaohongt]

Verified that our self host has dependency Owin self host and Startup.ce is removed from Owin self host