docs(frontend): added documentation about services

Closes #179

documentation/Application/Frontend/services.md

+# Frontend Services
+
+?> _In the contexts of software architecture, service-orientation and service-oriented architecture, the term service refers to a software functionality or a set of software functionalities (such as the retrieval of specified information or the execution of a set of operations) with a purpose that different clients can reuse for different purposes, together with the policies that should control its usage (based on the identity of the client requesting the service, for example). [Wikipedia](https://en.wikipedia.org/wiki/Service_(systems*architecture)*
+
+So the general idea of a _Service_ is to ease the developer experience by providing specialized "Software Blocks".
+
+## Available services in REX-DRI
+
+`REX-DRI` has several of such services, we will describe them here.
+
+### Navigation Service
+
+The purpose of this service is to ease the url / application change.
+
+```jsx
+import NavigationService from "...";
+
+function MyComponent() {
+  return <button onClick={() => NavigationService.goHome()}>Go Home</button>;
+}
+```
+
+This service gives you access to the main _routes_ of the application and a direct way to switch between them.
+
+_Check the detailed implementation to see what's possible._
+
+### Notification Service
+
+The purpose of this service is to ease the creation of notifications.
+
+As you can see below, as long as the app is created, you can create notifications super easily.
+
+```jsx
+import NotificationService from "...";
+
+function MyComponent({ message }) {
+  NotificationService.info(el.message);
+  return <></>;
+}
+```
+
+_Check the detailed implementation to see what's possible._
+
+### FullScreenDialog and Alert Services
+
+Those two services enable the use of the app's FullScreenDialog and Alert component (as there shouldn't be more than one of those at the same time in the app).
+
+```jsx
+import FullScreenDialogService from "...";
+import AlertService from "...";
+```
+
+_Check the detailed implementation to see what's possible._
+
+### Filter Service
+
+Well, this one is to handle university filtering logic outside of the components.
+
+### Data Services
+
+There are also several "Data Services":
+
+- CityService
+- CountryService
+- CurrencyService
+- LanguageService
+- UniversityService
+
+Those services should be used when you need to access this type of general data: they centralize conversions, joins, access by id, etc. So you can easily manipulate this data directly in the frontend / browser.
+
+## How those services are initialized
+
+### UI Services
+
+Most "UI Services" have their matching react component counterpart: `...ServiceComponent`. They are mounted and initialized [as soon the App](https://gitlab.utc.fr/rex-dri/rex-dri/-/blob/dev/frontend/src/entry/mainApp.jsx#L68) is created.
+
+### Data Services
+
+"Data services" are initialized as soon as the [`App` component](https://gitlab.utc.fr/rex-dri/rex-dri/-/blob/dev/frontend/src/components/app/App.jsx#L50) is loaded (and the necessary data has been loaded from the REST API).

documentation/_sidebar.md

@@ -27,7 +27,7 @@
     * [React basics](Application/Frontend/react.md)
     * [Use of Redux](Application/Frontend/redux.md)
     * [Tests](Application/Frontend/tests.md)
-    * [Notifications](Application/Frontend/notifications.md)
+    * [Services](Application/Frontend/services.md)
     * [Map](Application/Frontend/map.md)
     * [Troubleshooting](Application/Frontend/troubleshooting.md)