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/Animation/SkeletonHierarchy.cpp

@@ -63,7 +63,7 @@ int32 CHierarchy::FindNodeIndexByName(const char* name) const
 const CHierarchy::SNode* CHierarchy::FindNode(const char* name) const
 {
     int32 index = FindNodeIndexByName(name);
-    return index < 0 ? NULL : &m_nodes[index];
+    return index < 0 ? nullptr : &m_nodes[index];
 }
 
 void CHierarchy::CreateFrom(IDefaultSkeleton* pIDefaultSkeleton)