cost is Argument, but argument does not have to be cost.

* update function can not be inherited since updateImpl exsits
* remove update implementation in one inherited updater

* Check all files by pre commit hooks

* Fix sparse training for trainer_count=1

For trainer_count=1, the gradient machine is NeuralNetwork, which does not create parameter buf for PARAMETER_GRADIENT for sparse update in Parameter::enableType. But gradient parameter buf is still used in SgdThreadUpdater.

* Minor update to comment

* Correctly handling multiple inputs and integer inputs for recurrent_group

* Fix ScatterAgentLayer for generation

* Revert sequence_(nest)_rnn.conf

Sequences should be sorted according to the number of subsequences they have.

Change-Id: I8e0a8ea6fc2760652d9c76440a539c90860062d3

Change-Id: Id66da7b7f5bf9ec80cc19b347e4fb822a5a6f197

* by default, synchronize default_stream after resizeAndCopyFrom
* add sync in some places after resizeAndCopyFrom using other streams

Change-Id: Ia60c008a8c922f66e6b5e2ca3e488fc4625d6506