General cleanup of the FullSimLight Geant4 application

Before providing further, physics modelling related developments to the FullSimLight Geant4 application, a significant cleanup has been performed especially regarding the user actions. These were still identical to those that I developed as part of the fullCMS application (that FullSimLight is baed on) with the goal of demonstrating even some of the more advance user action features. These complex user actions make no much sense in case of FullSimLight and actually causing only limitations (e.g. cannot be utilised when the Pythia used primary generator is used instead of the gun). Therefore, the user actions have been greatly simplified in order to facilitate further developments. Only the mean number (per event) of charged/neutral simulation steps, track lengths, number of secondary electron, position and gamma particles are recorded.

The Pythia based primary generator option has also been fixed for proper seeding when using an MT built Geant4 with multiple worker threads. Each worker threads simulated exactly the same set of events before, while distinct subsets of a fixed set of events are processed by the individual workers. The original behaviour is kept now only when the application is executed in performance mode (i.e. with the -p flag).