Use find_packages() from setuptools

The current package list doesn't include periodically.managment and
periodically.migratinos, so these don't get installed and manage.py
doesn't see the "runtasks" command.

setuptools find_packages() automates finding all the correct
sub-packages
Convert to be timezone aware

Times returned by django are datetime aware if USE_TZ is turned on,
which it is by default.  periodically then crashes with "can't compare
offset-naive and offset-aware datetimes".

This converts instances of naive datetimes to be timezone enabled.
Everything is in UTC so it can be compared safely
Merge pull request #4 from ianw/timezone

Convert to be timezone aware