add GaussianDropout, GaussianNoise layers (#1894)
add GaussianDropout, GaussianNoise layers (#1894)

* add GaussianDropout, GaussianNoise layers, unit tests, python wrapper, module serializer unit test and docs
intel-analytics/BigDL,intel-analytics/BigDL,intel-analytics/BigDL,yangw1234/BigDL,yangw1234/BigDL,yangw1234/BigDL,yangw1234/BigDL,intel-analytics/BigDL