added product and divide operations on ContinuousFactor using ContinuousFactor.operate
added product and divide operations on ContinuousFactor using ContinuousFactor.operate

sandeepkrjha/pgmpy,abinashpanda/pgmpy,kris-singh/pgmpy,khalibartan/pgmpy,abinashpanda/pgmpy,ankurankan/pgmpy,pgmpy/pgmpy,kris-singh/pgmpy,ankurankan/pgmpy,sandeepkrjha/pgmpy,pgmpy/pgmpy,jhonatanoliveira/pgmpy,jhonatanoliveira/pgmpy,khalibartan/pgmpy