Master should create an event for unstopping jobs

Current Situation

• If a job is in PENDING state, it may be because it has been unstopped or it is just finishing a regular run. Currently there is no event for the specific transition to unstop a job, there's a general event only that results in the same PENDING taget state.

Desired Behavior

• A specific event should be raised when unstopping jobs (similar to unstopping job chains) that helps to distinguish if a PENDING state transition was performed due to an unstop operation.

Maintainer Notes

• This feature will be implemented with the JOC Cockpit Web Services, not with the JobScheduler Master. The nature of the requirement is to receive a notification about a state tansition which is not exactly what events in the Master are about. This feature will require to keep the previous state of a job (being stopped) in memory in order to decide if a state change to PENDING is a transition from a STOPPED status or from a RUNNING status. The implementation is therefore subject to a custom event that is provided by the JOC Cockpit Web Service that has better access to history information.