Implement event class #371
Description
Back in the day when we tried to implement a numpy array for the partilce list and could not do it because each event has a different number of particles, we did not think about implementing an Event class that could hold a numpy array of Particle objects inside and then we have an array of Events in the storer class.
This would also make other things easier.
The Event class could also store optional information about other event quantities like impact parameter, we could assign the centrality to it, ...
This would be a major change to the package and requires a lot of work (also for the analysis classes), but I wanted to keep this idea somewhere to not forget about it.