related with https://github.com/isce-framework/isce2/pull/97
+ move cpx cohe calculation code from main() to estCpxCoherence()
+ move computeCoherence import from the top to the inside of estCpxCoherence(), to avoid import error/warning sometimes.
+ fix typo in the default value of --cc option from 'fine.cori.full' to 'fine.cor.full'