Editor code: tidy up BOOLs,NULLs and overrides pt1.

A few 'typedefs' replaced by 'using's
This shouldn't have any functional changes at all, just c++17 modernization
It's a part 1 of a split #2847

Signed-off-by: Nemerle <nemerle5+git@gmail.com>

Code/Editor/Core/LevelEditorMenuHandler.cpp

@@ -80,12 +80,12 @@ namespace
             , m_trigger(trigger)
         {}
 
-        virtual ~EditorListener()
+        ~EditorListener() override
         {
             GetIEditor()->UnregisterNotifyListener(this);
         }
 
-        void OnEditorNotifyEvent(EEditorNotifyEvent event)
+        void OnEditorNotifyEvent(EEditorNotifyEvent event) override
         {
             m_trigger(event);
         }