Qualitative Trends plot: Exchange hyphen (-) for minus sign (−)

[TammoReinders]

In the plot for the qualitative trends increase, decrease and stability are represented by "+", "-", and "=" symbols. The decrease seems to be represented by a hyphen, that is placed lower and is less broad than a minus sign. -−

[SHorschBay]

Is resolved in the attached branch. Can be closed as soon it is validated and incorporated in main.