rework Task Overview

Empty Task checks added
shorter ETE line
forgot to reenable SetVisible
fix eqMC calculation :
	"MC = Vso*[ (V/Vo)^3 - (Vo/V)]" formula is wrong.

polar equation is Vs = a*V² + b*V + c, so eqMC equation is

    MC = c - a*V²
Merge branch 'eqMC' of https://github.com/brunotl/LK8000 into bruno