The big NULL replacement party part 1.

This is meant to be a safer alternative since
NULL can often be 0. Let's not rely on that.

And yes, I know this is a lot of files. This is
a safer thing to do in big commits vs for loops.

src/StepsUtil.cpp

@@ -123,7 +123,7 @@ void StepsUtil::SortStepsPointerArrayByNumPlays( vector<Steps*> &vStepsPointers,
 		}
 	}
 
-	ASSERT( pProfile != NULL );
+	ASSERT( pProfile != nullptr );
 	for(unsigned i = 0; i < vStepsPointers.size(); ++i)
 	{
 		Steps* pSteps = vStepsPointers[i];