Set up the auto-clean periodic task

[bochecha]

Note: this is to be done in addition to the cron job Ideascube already has.

Because RFI boxes will be left alone without a Linux-savvy admin or an Internet access for 3 years, it's possible that the disk might get full eventually.

So we've made a command which can remove all the old radio shows and messages/ads from the audience.

Simply run the command:

$ ideascube irfi-auto-clean 6

The above will remove the stuff older than 6 months. Use a different number of months if appropriate.

This can probably be run daily.