Returns the list of *dictionnaries* for which the accounts are
        accessibles by ``request.user`` filtered by ``roles`` if present.

def get_accessibles(request, roles=None):
        """
        Returns the list of *dictionnaries* for which the accounts are
        accessibles by ``request.user`` filtered by ``roles`` if present.
        """
        results = []
        for role_name, organizations in six.iteritems(request.session.get(
                'roles', {})):
            if roles is None or role_name in roles:
                results += organizations
        return results