* Move cart's form from carts/views.py to carts/forms.py.
* Add url field to ChosenReward model.
* Use new ChosenReward url field in profile view.
* Add new configuration option WOO_REG_OPTIONS_INFO_FILE that
  specifies the registration options available in the middleware.
* Remove not used WOO_CART_xxx configuration options.
* Define new registration URLs in middleware/urls.py.
* Add example configuration file registration_options.yml.

Signed-off-by: Birin Sanchez <birin.sanchez@puri.sm>