Improve alascan output

[mgiulini]

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Closes #866 by:

• changing the plot title
• changing the sign of the deltas
• removing the ori_score field, that was containing the difference between the emscoring score of the mutant and the existing score attribute of the wildtype (potentially coming from any module). This does not make much sense, as the only thing that matters is the difference between the two emscoring values