Migration to Tryton 2.6 Active Record pattern

* Bump version to 2.6.0.1dev
* Adds audit and xmltests command to setup.py.
* Refactored test cases to install company module first and then
  install the nereid_cart_b2c.
* Remove sale, invoice and shipment method from Website as they should
  have their own handlers in the corresponsing models.