[script.evaluate] Fix second-annotator comparisons with a key-resemblance check; Add assertions in engine.evaluator to ensure proper comparisons

[script,engine,test] Allows the user to specify the number of steps for threshold/performance analysis

[utils.metric] Rename as measure as some of the values are not real metrics; Add tests for AUC and improve its implementation

[script.*] Implement F1-score a priori where possible; Improve plotting of precision-recall curves with better legends, more consistence; Remove redundant plotting code; Update tests