New features and fixes for the retry option

[leandernikolaus]

• Retry can be used with threshold failures.
• Only access failures are safe in the retry structs history.
• The output struct indicates if an output is the result of a retry
• A config option was added to determine if retries cause time to increase. Default option is retires do not cost time.
• If the uniqueChunk per iteration option is used, the output worker may receive more outputs than Iterations, since retries cause outputs, but do not count towards iterations. The output/worker is adjusted to ensure a log statement at the end of the experiment. Additional unrelated feature included is some more metrics for income of originators. First I try to compute the gini coefficient to see how fair the prices are, i.e. if some originators pay more for downloading than other. Second I compute the gini coefficient over a metric that combines both income and download utility of originators. Download utility is computed as maximum (chunk price - payed chunk price) per chunk.