Improve label for aliases in "Filter by Activity" and use of new-style

EntityRepository for ActivityType

* [activity][export] Feature: improve label for aliases in "Filter by activity type"
* [activity][export] DX/Feature: use of an `ActivityTypeRepositoryInterface` instead of the old-style EntityRepository

src/Bundle/ChillActivityBundle/Entity/ActivityType.php

@@ -516,6 +516,11 @@ class ActivityType
         return $this->userVisible;
     }
 
+    public function hasCategory(): bool
+    {
+        return null !== $this->getCategory();
+    }
+
     /**
      * Is active
      * return true if the type is active.