[ADD] new module sale_pricelist_restrict_product_in_so

thanks @veloutin who was the original author of this module
@bwrsandman done ! but my PyCharm is more restrictive than Flake8:

  Name     :  test_product_pricelist_restrict.py
 Location      file [new-oe-sandy] - .../git/sale-workflow/sale_pricelist_restrict_product_in_so/tests/test_product_pricelist_restrict.py
Problem synopsis      Function name should be lowercase (at line 33)