Cleans up ext methods and where they are located and what they call to ensure dependencies are taken care of, cleans up Startup, moves routing appropriately

src/Umbraco.Web.Website/Extensions/UmbracoWebsiteApplicationBuilderExtensions.cs

@@ -0,0 +1,27 @@
+using System;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.Extensions.DependencyInjection;
+using SixLabors.ImageSharp.Web.DependencyInjection;
+using Umbraco.Core;
+using Umbraco.Extensions;
+using Umbraco.Web.Common.Middleware;
+
+namespace Umbraco.Web.Website.Extensions
+{
+    public static class UmbracoWebsiteApplicationBuilderExtensions
+    {
+        public static IApplicationBuilder UseUmbracoWebsite(this IApplicationBuilder app)
+        {
+            if (app == null) throw new ArgumentNullException(nameof(app));
+
+            if (!app.UmbracoCanBoot()) return app;
+
+            // Important we handle image manipulations before the static files, otherwise the querystring is just ignored.
+            // TODO: Since we are dependent on these we need to register them but what happens when we call this multiple times since we are dependent on this for UseUmbracoBackOffice too?
+            app.UseImageSharp();
+            app.UseStaticFiles();
+
+            return app;
+        }
+    }
+}