Reorder BranchNodeData struct members to make it more compact

By simply putting two bool fields consecutively to each other, we reduce
the number of bytes of padding used from 6 to 2 in a typical 32 bit
build, saving 4 (or 8, in 64 bits) bytes per branch item.

src/generic/datavgen.cpp

@@ -615,12 +615,12 @@ private:
         // Is the branch node currently open (expanded)?
         bool                 open;
 
-        // By which column are the children currently sorted
-        int                  sortColumn;
-
         // Are the children currently sorted ascending or descending
         bool                 sortAscending;
 
+        // By which column are the children currently sorted
+        int                  sortColumn;
+
         // Total count of expanded (i.e. visible with the help of some
         // scrolling) items in the subtree, but excluding this node. I.e. it is
         // 0 for leaves and is the number of rows the subtree occupies for