Fixed the equality compare of MeshFilter class in PythonAPI
Created by: wuwenbin2006
For creating multiple MeshFilters , OpenMOC pythonAPI will take them the same if they have the same mesh dimensions but different lower_left and upper_right. This is because the eq is too simple in the base class Filter. And the wrong equality affects the _create_filter_subelements(tallies.py:3149) called by Tallies::export_to_xml().
Just override the eq and hash in class MeshFilter.