Create WebApplication class for starting web apps application entry points (static void Main)

[DamianEdwards]

Create a new type that will be called from web applications in their static void Main(string args). Note this depends on #425

public static class WebApplication
{
    public static void Start<TStartup>()
    {
        Start(typeof(TStartup), null);
    }

    public static void Start<TStartup>(string[] args)
    {
        Start(typeof(TStartup), args);
    }

    public static void Start(Type startupType)
    {
        Start(startupType, null);
    }

    public static void Start(Type startupType, string[] args)
    {
        // Basically the body of Microsoft.AspNet.Hosting.Program.Main, which will now call into this instead
        ...
    }
}