Refactor tags services and added tests

Implemented some functionality which will allow the service
configuration of the app to be split among the features for readability
and testability.

src/service.rs

@@ -0,0 +1,16 @@
+use actix_web::App;
+
+pub trait ServiceBuilder<T> {
+    fn add_feature<F>(self, f: F) -> App<T>
+    where
+        F: Fn(App<T>) -> App<T>;
+}
+
+impl<T> ServiceBuilder<T> for App<T> {
+    fn add_feature<F>(self, create_feature: F) -> App<T>
+    where
+        F: Fn(App<T>) -> App<T>,
+    {
+        create_feature(self)
+    }
+}