Editor code: tidy up BOOLs,NULLs and overrides pt5. (#2876)

A few 'typedefs' replaced by 'using's
This shouldn't have any functional changes at all, just c++17 modernization
It's a part 5 of a split #2847

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

Co-authored-by: Nemerle <nemerle5+git@gmail.com>

Code/Editor/ConfigGroup.h

@@ -37,11 +37,11 @@ namespace Config
             , m_description(szDescription)
             , m_type(varType)
             , m_flags(flags)
-            , m_ptr(NULL)
+            , m_ptr(nullptr)
         {};
 
         virtual ~IConfigVar() = default;
-        
+
         ILINE EType GetType() const
         {
             return m_type;