Moved service to own class an added includes

This commit moves the management of the cron service into it's own class as well
as adding support for Suse the in case statement for working out the name of the
cron service.

The init.pp / main cron class now includes the various other cron classes for
managing other crontabs so the user can simply 'include cron' rather than
'include cron, include cron::daily, etc...'.