Fix Visualization: Mann-Whithey-U-Statistics

[amtsvch]

Is-state:
Now two statistics are computed in RCA for the call trees: t-score and Mann-Whitney p-score. Node colours, that denote change, are set according to their t-scores. Also only t-value is shown in tree overview.

To-be-state:

• Nodes colours are set according to Mann-Whitney.
• Mann-Whitney score is also shown in the overview.

Nice-to-have:

• It would be actually nice to have an option to switch between chosen statistics in the call tree, if more than one were computed.