8.4.9 correlate(self,phase=-1,channel=1,plot=1):

correlate $<$ DataAna(BoaDataEntity.DataEntity): $<$ BoaDataAnalyser.py

    NAM: correlate (method)  
    DES: compute correlation factor relative to given reference channel
         for given phase
    INP: 
	 (i) channel  =  reference channel against which correlated
         (i) phase    =  0,1,2
         (l) plot     =  1 or 0; overwrite Data_Red with fit?
    OUT: (f) data     =  overwrites Data_Red_p with fit
             FFCF_CN  =  rank-1 flat field with respect to channel