Paginate results of Courses API list endpoint

* Catalog results are now paginated
* Implements the new namespaced pagination described at
  https://openedx.atlassian.net/wiki/pages/viewpage.action?pageId=47481813
* API level code returns pythonic business objects
* View layer performs serialize at the view layer
* Convert views to use DRF generic views
* Removes an unintentional authentication decorator that caused
  the detail endpoint to return a 401 for anonymous users

MA-1724

openedx/core/lib/api/paginators.py

@@ -29,6 +29,38 @@ class DefaultPagination(pagination.PageNumberPagination):
         })
 
 
+class NamespacedPageNumberPagination(pagination.PageNumberPagination):
+    """
+    Pagination scheme that returns results with pagination metadata
+    embedded in a "pagination" attribute.  Can be used with data
+    that comes as a list of items, or as a dict with a "results"
+    attribute that contains a list of items.
+    """
+
+    page_size_query_param = "page_size"
+
+    def get_paginated_response(self, data):
+        """
+        Annotate the response with pagination information
+        """
+        metadata = {
+            'next': self.get_next_link(),
+            'previous': self.get_previous_link(),
+            'count': self.page.paginator.count,
+            'num_pages': self.page.paginator.num_pages,
+        }
+        if isinstance(data, dict):
+            if 'results' not in data:
+                raise TypeError(u'Malformed result dict')
+            data['pagination'] = metadata
+        else:
+            data = {
+                'results': data,
+                'pagination': metadata,
+            }
+        return Response(data)
+
+
 def paginate_search_results(object_class, search_results, page_size, page):
     """
     Takes edx-search results and returns a Page object populated

openedx/core/lib/api/tests/test_paginators.py

@@ -1,10 +1,15 @@
 """ Tests paginator methods """
+
+from collections import namedtuple
+
 import ddt
 from mock import Mock, MagicMock
 from unittest import TestCase
 from django.http import Http404
+from django.test import RequestFactory
+from rest_framework import serializers
 
-from openedx.core.lib.api.paginators import paginate_search_results
+from openedx.core.lib.api.paginators import NamespacedPageNumberPagination, paginate_search_results
 
 
 @ddt.ddt
@@ -118,6 +123,50 @@ class PaginateSearchResultsTestCase(TestCase):
             paginate_search_results(self.mock_model, self.search_results, self.default_size, page_num)
 
 
+class NamespacedPaginationTestCase(TestCase):
+    """
+    Test behavior of `NamespacedPageNumberPagination`
+    """
+
+    TestUser = namedtuple('TestUser', ['username', 'email'])
+
+    class TestUserSerializer(serializers.Serializer):  # pylint: disable=abstract-method
+        """
+        Simple serializer to paginate results from
+        """
+        username = serializers.CharField()
+        email = serializers.CharField()
+
+    expected_data = {
+        'results': [
+            {'username': 'user_5', 'email': 'user_5@example.com'},
+            {'username': 'user_6', 'email': 'user_6@example.com'},
+            {'username': 'user_7', 'email': 'user_7@example.com'},
+            {'username': 'user_8', 'email': 'user_8@example.com'},
+            {'username': 'user_9', 'email': 'user_9@example.com'},
+        ],
+        'pagination': {
+            'next': 'http://testserver/endpoint?page=3&page_size=5',
+            'previous': 'http://testserver/endpoint?page_size=5',
+            'count': 25,
+            'num_pages': 5,
+        }
+    }
+
+    def setUp(self):
+        super(NamespacedPaginationTestCase, self).setUp()
+        self.paginator = NamespacedPageNumberPagination()
+        self.users = [self.TestUser('user_{}'.format(idx), 'user_{}@example.com'.format(idx)) for idx in xrange(25)]
+        self.request_factory = RequestFactory()
+
+    def test_basic_pagination(self):
+        request = self.request_factory.get('/endpoint', data={'page': 2, 'page_size': 5})
+        request.query_params = {'page': 2, 'page_size': 5}
+        paged_users = self.paginator.paginate_queryset(self.users, request)
+        results = self.TestUserSerializer(paged_users, many=True).data
+        self.assertEqual(self.expected_data, self.paginator.get_paginated_response(results).data)
+
+
 def build_mock_object(obj_id):
     """ Build a mock object with the passed id"""
     mock_object = Mock()