More robust average and peak PQ/CQ

Jop Wolffsrequested to merge
github/fork/hbrmn/develop into develop

Created by: hbrmn

This commit is based on a suggestion from jtrebosc and calculates the average PQ value for a given Czjzek distribution more pythonic and displays average and peak CQ/PQ values in the Czjzek distribution plot.

The result should look like this:

image

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