Adding an `ObjectManager` base class.
Splitting off the GAE queryset bits and packing it into an object manager.
Moving the object manager out of base as that will be overwritten by the following merge.
Adding two more object managers.
Slight adjustments to the paginator.
Slight adjustment for the GAE DB object manager. All tests pass now.
Using the `GaeUnifiedPaginator` for the tests. They pass. Still need to move this paginator though.
Making sure no normal list is used for our paginator.
Making ndb object manager work.
Cleaning up and commenting.
Adding proper paginators for these managers.
Writing some tests.
Making sure we invalidate cached cursors.
Adding a few more comments.
Merge branch 'refs/heads/separate_object_managers' into filterable_paginator

Conflicts:
	object_managers/base.py
	object_managers/ndb_api.py