Go through HPAGroups and store the distro of ordinal values of 
       quality scores

def analyze_quality(self):
    """Go through HPAGroups and store the distro of ordinal values of 
       quality scores"""
    res = {}
    for h in self._hpas:
      if h.type() not in res: res[h.type()]={}
      for c in h.get_quality():
        if c not in res[h.type()]: res[h.type()][c] = 0
        res[h.type()][c]+=1
    self._quality_distro = res