Spectrum Analyzer : make timing of delayed peaks dependent on sensitivity

[blaubär]

Situation : the delay time and the drop velocity are constant and don't depend on the sensitivity

Problem : this doesn't feel natural when the spectrum has been smoothed by a low sensitivity, one would then expect a longer delay time and a slower drop velocity

Proposal : optionally make the delay time and drop velocity dependent on the sensitivity, a lower sensitivity should induce a longer delay time and a slower drop velocity