Revert "Remove unused Error.cshtml"

This reverts commit 7b2ef9aec2.

BTCPayServer/Controllers/HomeController.cs

@@ -14,5 +14,24 @@ namespace BTCPayServer.Controllers
         {
             return View("Home");
         }
+
+        public IActionResult About()
+        {
+            ViewData["Message"] = "Your application description page.";
+
+            return View();
+        }
+
+        public IActionResult Contact()
+        {
+            ViewData["Message"] = "Your contact page.";
+
+            return View();
+        }
+
+        public IActionResult Error()
+        {
+            return View(new ErrorViewModel { RequestId = Activity.Current?.Id ?? HttpContext.TraceIdentifier });
+        }
     }
 }