Paster command that can be run in a cron

This is definitely not perfect but will do the job. Things that need to be fixed before we merge this into the datastore extension, but this should do for now.
- [x] Use the get_action commands for the datastore API.  I haven't done this yet, because it was useful for debugging not to do that.
- [x] Check existence of site_url and fail if it isn't set.  Only ever a problem with developer sites, I'd think, so it's not a big deal for SA. **This is no longer required since I use get_action() directly.