* Basic mean normalization

* Add NVM to serializer

* Add test for mean normalization

* Add support for across_channel atribute

* Add test for mvn_mean_normalization splited by channels

* Assume that data have n and c channels

* Add support for normalize_variance attribute

* Add test for full mean variance normalization

* Add type prop test

* Skip tests on GPU

* Use ngraph builder functions instead of my own

* Update mvn.cpp

* Change order in initializer list

* Review fix