Order by post number should be chronological
The FEC should be ordered chronologically by the post number [1]. For now, we order by "post_number ASC" but if the numbering is not padded, it does not result in a chronological order.
I propose to fix the order of post_number like we did to order the party code.
[1] https://groups.google.com/d/msg/tryton-fr/YbciH4rTptE/a5K1DgPaBgAJ