Drop jslint from Makefile
Use head version of django-nose for Django 1.7 compat
Add sample app, coverage to 100%, refactors

* Added a sample app (sample_poll_app) based on the Django tutorial.
* Moved test implementation of BaseCache to the new app
* Added tests to bring coverage to 100%
* Renamed PkOnlyValuesList to PkOnlyQueryset
* PkOnlyQueryset.values_list now returns list of pks, not a
  PkOnlyQueryset.  This means __getitem__ is unused, so dropped.
* drf_cached_instances/settings.py deleted, incompatible with testing
* Default to DEBUG=1