Implement HasCentersInterface in Household class (will fix access control)

The Household class now implements the HasCentersInterface and includes a method to get all centers associated with current persons in the household. This enhancement will allow fetching of all household-associated centers easier.

src/Bundle/ChillMainBundle/Entity/Center.php

@@ -82,10 +82,7 @@ class Center implements HasCenterInterface, \Stringable
         return $this->groupCenters;
     }
 
-    /**
-     * @return int
-     */
-    public function getId()
+    public function getId(): null|int
     {
         return $this->id;
     }