Get project ready for PyPI packaging and deployment

This pull request incorporates various changes to allow our project to be packaged for PyPI and deployed. Here is a quick summary of the changes:

- Add configuration file (/etc/megacron.conf) to specify location of db.p
- Add console scripts (megacrontab, megacrond, megacron-status)
- Dependencies will automatically get installed
- Remove python-crontab as a dependency (just use croniter)
- Update README to explain how this all works

The only issue I know of is that regular users can't edit their own crontab, only root can.