Use Minuit to automatically determine ASq max for signal in LauIsobarDynamics

Summary:
As described in T202, currently the maximum value of ASq (used for the accept/reject method of toy generation) for a given DP model has to be determined by trial and error and then set by hand.

This revision repurposes the LauFitter class to optimise ASq rather than a likelihood function:
ASqMax is found by minimising -ASq w.r.t. m13Sq and m23Sq.
This is done from multiple starting points: at cos(helicity) = -1, 0, 1 and m = m0 - Gamma0, m0, m0 + Gamma0
for each component in the model (resonant and nonresonant).

We intend to extend this to time-dependent models later.

This revision also takes the opportunity to perform some modernisation of some of the affected classes.

Test Plan: This has been tested and works successfully in GenFit3pi, GenFit3K and GenFitBelleCPKpipi

Reviewers: jback

Reviewed By: jback

Subscribers: tlatham, andylhcb

Tags: Laura

Differential Revision: https://phab.hepforge.org/D85