Added services

This commit moves most controller logic onto Services. Services are part of the Service-Repository pattern. The models act as repositories.

Services are easily testable and are needed for the upcoming API, in order to avoid duplicated code and to maintain a single source of "truth".

 The User, Vacancy and Vote controllers still need their logic moved onto services.

app/Http/Controllers/DashboardController.php

@@ -27,6 +27,8 @@ use App\Vacancy;
 
 class DashboardController extends Controller
 {
+    // Note: The dashboard doesn't need a service because it doesn't contain any significant business logic
+
     public function index()
     {
         $totalPeerReview = Application::where('applicationStatus', 'STAGE_PEERAPPROVAL')->get()->count();