Mailer project continued:

Mailer project continued:
- Refactured FILTER_ORDER_ZIP_CODE_SQL() to allow also zip code member inclusion
  through GET parameters. This can be used e.g. in what=list_user&zip=12345 to
  only list members from zip code 12345
- Some todos added for what-list_user.php: please refacture birthday handling
  and link generation
- TODOs.txt updated