Pause/Resume features

I added these features to the plugin:
- Ability to pause/resume all of the workers on this node.
- Ability to pause/resume all of the workers across the whole the cluster.
- Ability to check if all of the workers in the cluster are paused.
- Ability to shutdown all of the workers in the cluster.
- Ability to start all of the workers on this node in the paused state.

I would love to get these fetures officially into the Grails Jesque plugin. 

The complete background and rationale can be found in this thread: https://github.com/gresrun/jesque/issues/24

Thanks!