Coding standards

The attached patch brings the 5.x version (will be ported to 6.x shortly) to compliance with the coding standards.

In addition, it makes, IMHO, the admin interface much cleaner (must clear the menu cache) by using radios and checkboxes (hence added a css file). I altered the intervals a bit. There were several strings that were not translatable so I wrapped them in t(). I added some descriptive text to the list.

One should not, as a friend recently discovered, allow a module like this to fire its cron code before the adopter is fully aware of what they're doing. So I set the default cron interval to 0, for "manual only" and added code to check for that.