LibCore: Make CSocket's notifiers into children of the CSocket

The Inspector app quickly exposes crappy flat object hiearchies without
parent/child relationships. This is one of many commits that improves
the situation by making parent/child CObject relationships explicit.

Libraries/LibCore/CNotifier.h

@@ -12,7 +12,7 @@ public:
         Write = 2,
         Exceptional = 4,
     };
-    CNotifier(int fd, unsigned event_mask);
+    CNotifier(int fd, unsigned event_mask, CObject* parent = nullptr);
     virtual ~CNotifier() override;
 
     void set_enabled(bool);