change order in PreTest, show all Histos

the order is important in PreTest
  setVana(); // setting this later would change thresholds
  setVthrCompId(); // setting this later would change the timing
  setCalDel(); // step three

fHistList.clear(); is called once, at the beginning.
PreTest now produces histos from all three steps

added two steering parameters: noiseWidth and noiseMargin

-- Pretest
targetIa       24
setVana        button
noiseWidth     22
noiseMargin    15
setVthrCompId  button
PIX1           11,20 
Ntrig          10
setCalDel      button
SaveDacs       button