API updates

- Move all generic API classes definitions to the rest_api.generics
module.
- Update API status code on insufficient access for the apps:
indexes, parsing, documents, metadata, ocr, permission,
user management.
- Update API tests.

Signed-off-by: Roberto Rosario <roberto.rosario@mayan-edms.com>

mayan/apps/checkouts/api_views.py

@@ -1,9 +1,8 @@
 from __future__ import absolute_import, unicode_literals
 
-from rest_framework import generics
-
 from mayan.apps.acls.models import AccessControlList
 from mayan.apps.documents.permissions import permission_document_view
+from mayan.apps.rest_api import generics
 
 from .models import DocumentCheckout
 from .permissions import (