Added placeholder users; Better exception handling; Enhanced local setup

lang/en/exceptions.php

@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+use App\Exceptions\Api\TimeEntryStillRunningApiException;
+use App\Exceptions\Api\UserNotPlaceholderApiException;
+
+return [
+    'api' => [
+        TimeEntryStillRunningApiException::KEY => 'Time entry is still running',
+        UserNotPlaceholderApiException::KEY => 'The given user is not a placeholder',
+    ],
+];