Aggregate msrm_sampl to config option

Measurement sampling for xovers computation (msrm_sampl) is currently scattered between the following files acting on rough and fine xovs, and needs to be manually set-up consistently, which is sub-optimal xov_setup.py l.80-85

if XovOpt.get("instrument") in ['BELA', 'CALA']:  
    self.msrm_sampl = 20  # WD: try 10
else:
    self.msrm_sampl = 4

and xov_prc_iters l.28-31

if xov_iter==0:
    msrm_smpl = 4 # same as used for rough_xovs in PyXover (should be automatic)
else:
    msrm_smpl = 4  # should be even...

Aggregate to a single option in config.py

steo85it / pyxover

Aggregate msrm_sampl to config option #13