Allow default editor to be configurable

Migrated from: https://tracker.clearos.com/view.php?id=5252

Reported by: Marc Laporte

The issue was titled "Nano should be the default editor (for things like crontab, commit messages, etc.)" on the old issue tracker.

While I agree with the sentiment it is a matter of personal preference. Perhaps a better option would be to allow the root user to select the default editor from the base installed ones (at least vi and nano) or specify a custom one.