HTML rendering support for the Website service (#5)

This PR contains the work done to replace the use of static _HTML_ files with type-safe HTML rendered server-side via **Elementary** through **Hummingbird**.

To provide further details about the work done:

* Added the **Elementary** dependencies.
* Added the `IndexPage` and `ErrorPage` pages, ported from the old HTML boilerplate; removed the static files.
* Added the `RootController` controller serving GET / using the `IndexPage` page, wired into the router.
* Reworked the `NotFoundMiddleware` middleare to render `ErrorPage` page directly; non-notFound errors still propagate.
* the `FileMiddleware` middleware no longer searches for any static `index.html` file.
* Simplified the `StaticFile` enumeration, dropped unused constants and now-unnecessary throws.

Reviewed-on: rock-n-code/loud-amsterdam#5
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>

Services/Website/Package.swift

@@ -19,6 +19,14 @@ let package = Package(
         )
     ],
     dependencies: [
+        .package(
+            url: "https://github.com/elementary-swift/elementary.git",
+            from: "0.6.0"
+        ),
+        .package(
+            url: "https://github.com/hummingbird-community/hummingbird-elementary.git",
+            from: "0.3.0"
+        ),
         .package(
             url: "https://github.com/hummingbird-project/hummingbird.git",
             from: "2.25.0"
@@ -55,10 +63,18 @@ let package = Package(
                     name: "Configuration",
                     package: "swift-configuration"
                 ),
+                .product(
+                    name: "Elementary",
+                    package: "elementary"
+                ),
                 .product(
                     name: "Hummingbird",
                     package: "hummingbird"
                 ),
+                .product(
+                    name: "HummingbirdElementary",
+                    package: "hummingbird-elementary"
+                ),
             ],
             path: "Sources/Library"
         ),
@@ -77,6 +93,18 @@ let package = Package(
             name: "WebsiteCoreTests",
             dependencies: [
                 .byName(name: "WebsiteCore"),
+                .product(
+                    name: "Elementary",
+                    package: "elementary"
+                ),
+                .product(
+                    name: "Hummingbird",
+                    package: "hummingbird"
+                ),
+                .product(
+                    name: "HummingbirdTesting",
+                    package: "hummingbird"
+                ),
             ],
             path: "Tests/Library"
         ),