Editor code: tidy up BOOLs,NULLs and overrides pt3.

A few 'typedefs' replaced by 'using's
This shouldn't have any functional changes at all, just c++17 modernization
It's a part 3 of a split #2847

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

Code/Editor/TrackView/SequenceBatchRenderDialog.h

@@ -81,8 +81,8 @@ protected:
         bool disableDebugInfo;
         bool bCreateVideo;
         SRenderItem()
-            : pSequence(NULL)
-            , pDirectorNode(NULL)
+            : pSequence(nullptr)
+            , pDirectorNode(nullptr)
             , disableDebugInfo(false)
             , bCreateVideo(false) {}
         bool operator==(const SRenderItem& item)
@@ -155,7 +155,7 @@ protected:
             , expectedTotalTime(0)
             , spentTime(0)
             , flagBU(0)
-            , pActiveDirectorBU(NULL)
+            , pActiveDirectorBU(nullptr)
             , cvarCustomResWidthBU(0)
             , cvarCustomResHeightBU(0)
             , cvarDisplayInfoBU(0)