move_column_after
Description:
Moves column to be after to base_column.
 If base_column is null, then column is placed in the first position.
Parameters:
| this | 
           A TreeView  | 
      
| column | 
           The TreeViewColumn to be moved.  | 
      
| base_column | 
           The TreeViewColumn to be moved relative to, or null.  |