remove extreme values (outliers) from display parameter mapping range

[diemoschwarz]

there's sometimes an annoying segment with -240dB wrecking the color/size scale

• [ ] add an outlier percentage to camu.menu, rounding up the number of outliers to remove, i.e. when >0 at least the min/max values will be removed
• [ ] adapt display param mapping to use next smaller occuring values for mapping range
• [ ] probably useful for all display params
  • but how could this work for x/y?