Implement change-based metrics

[wrigleyDan]

Change needs to be quantified when comparing query results.

The following metrics are implemented:

• Rank-biased overlap
• Jaccard

Both metrics can be are calculated for a specific depth which is configurable.

Metrics are calculated per query. Always, two result sets are compared. Per query both metrics calculations take two result sets as their input and return the metrics (a decimal in the range between 0 and 1).