'Return groups used to classify recipients of a notification email.
Groups is a list of tuple containing of form (group_name, group_func,
group_data) where
* group_name is an identifier used only to be able to override and manipulate
groups. Default groups are user (recipients linked to an employee user),
portal (recipients linked to a portal user) and customer (recipients not
linked to any user). An example of override use would be to add a group
linked to a res.groups like Hr Officers to set specific action buttons to
them.
* group_func is a function pointer taking a partner record as parameter. This
method will be applied on recipients to know whether they belong to a given
group or not. Only first matching group is kept. Evaluation order is the
list order.
* group_data is a dict containing parameters for the notification email
* has_button_access: whether to display Access <Document> in email. True
by default for new groups, False for portal / customer.
* button_access: dict with url and title of the button
* has_button_follow: whether to display Follow in email (if recipient is
not currently following the thread). True by default for new groups,
False for portal / customer.
* button_follow: dict with url adn title of the button
* has_button_unfollow: whether to display Unfollow in email (if recipient
is currently following the thread). True by default for new groups,
False for portal / customer.
* button_unfollow: dict with url and title of the button
* actions: list of action buttons to display in the notification email.
Each action is a dict containing url and title of the button.
Groups has a default value that you can find in mail_thread
_message_notification_recipients method.'

@api.multi
def _notification_recipients(self, message, groups):

    return groups
