* add layernorm to bert
* add layernorm test
* add layernorm test with load state dict
* add use_mixedfusedLN in shard config
* refactor policy to support fused_layernorm
* add dropout layer, add dropout test
* modify seed manager as context manager
* add a copy of col_nn.layer
* add dist_crossentropy loss; separate module test
* polish the code
* fix dist crossentropy loss
* add dropout layer, add dropout test
* modify seed manager as context manager
* add a copy of col_nn.layer
* add dist_crossentropy loss; separate module test
* polish the code
* fix dist crossentropy loss