Expose underlying job in GrailsJob

In order for the quartz-monitor Grails plugin to function error-free with StatelessGrailsJob (see https://github.com/jamescookie/quartz-monitor/blob/master/src/groovy/grails/plugins/quartz/QuartzDisplayJob.groovy#L30), the underlying job needs to be exposed.  There might be a different way to fix this issue in the quartz-monitor plugin, but this seemed like the least impactful way to resolve it.