Editor code: tidy up BOOLs,NULLs and overrides pt4.

A few 'typedefs' replaced by 'using's
This shouldn't have any functional changes at all, just c++17 modernization
It's a part 4 of a split #2847

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

Code/Editor/Util/bitarray.h

@@ -74,7 +74,7 @@ public:
         void flip() {* p ^= mask; }
     };
 
-    CBitArray() { m_base = NULL; m_bits = NULL; m_size = 0; m_numBits = 0; };
+    CBitArray() { m_base = nullptr; m_bits = nullptr; m_size = 0; m_numBits = 0; };
     CBitArray(int numBits)    { resize(numBits); };
     ~CBitArray()
     {