Move visitor to another package

kosapi/entity/fields/base_field.py

-from kosapi import visitor
+from kosapi.utils import visitor
 class DescriptorAutoNameMeta(type):

kosapi/parser/field_visitor_content.py

-from kosapi import visitor
+from kosapi.utils import visitor
 from kosapi.entity.fields import BaseField, XLinkFieldProxy
 from kosapi.entity_factory import EntityFactory
 from kosapi.parser.lxml import get_attr_namespace, remove_namespace_from_string

kosapi/parser/field_visitor_meta.py

-from kosapi import visitor
+from kosapi.utils import visitor
 from kosapi.entity.fields import BaseMetaField
 from kosapi.settings import XML_NAMESPACES as NSMAP

kosapi/visitor/visitor.py → kosapi/utils/visitor/visitor.py

-from kosapi.visitor.visitable import Visitable
+from kosapi.utils.visitor.visitable import Visitable
 class Visitor:
     VISITED_CLASS = None

tests/visitor/test_visitor.py

 import unittest
-from kosapi import visitor
+from kosapi.utils import visitor
 class DummyVisitableBase(visitor.Visitable): pass