introduce loglevels and make prints in SyncSimulatedPayment Session optional

[renepickhardt]

As discussed with @sebulino the payment session currently computes a lot of statistics and depicts them to the user via the command line. However it is pretty pointless if one wants to automate tests, conduct full simulations and automatically evaluate the computed statistics.

I think it would be great to introduce a logging framework and make the outputs optional depending on the loglevel (and potentially to a log file instead of cli) also it might make sense to return the statistics of the paymentsession in a json dict that can be evaluated automatically in a simulation setting.