fixes Bug 950735 (v72) -  refactor crontabber to use the transaction_executor

looking through the code of the of the crontabber with an eye toward deprecation of old APIs, I find that crontabber could benefit from the use of the TransactionExecutor classes.  That will disambiguate when transactions start and stop, and always ensure that a transaction is closed properly.  

This change will also prepare crontabber to participate the configman resource branch project.  Each crontabber job will declare its configuration with regards to database access rather than relying on the existence of an external [database] section.  Configman will create an equivalent in [resources][[postgresql]] and allow any individual cron job to locally override the values.

This covers just the crontabber itself, not the jobs.  They will have their own bugs filed for conversion.