Provide data base backed storage for deployments

Currently jbpm-kie-services provide deployment service that allows to put units into runtime (essentially create RuntimeManager for them) but does not preserve these units between server restarts. Instead it just fires events so the requesting component shall take care of that. This issue is about to provide data base backed storage that will come out of the box and can be used instead of forcing users to build their own.
Just for completeness, kie-wb/jbpm-console uses system.git repository for that purpose.

Solution should provide:
Event observers for deploy and undeploy events of deployment service
Listener that is capable to reload all units on application startup and react on events to support clustered solutions.