DalitzKinematics: plotting phsp contours; adding phsp contours to
DalitzPlotterApp; bug in s2max, s2min..etc: didn't really fix it but i
wrote a new funtion mimin&mimax that provides min max value of s1,s2,s3
given any invariant mass. This is used for contour plotting and seems to
work; AmpWigner: changing invariant masses in calculation of helicity
angle, JPSI->gamma pi0pi0 can now be produced without error!
Merge branch 'master' of github:MathiasMichel/ComPWA