1. v2.layer.parse_network does not correctly handle the generation output.
2. GatherAgentLayer does not correctly handle generation output when batch_size > 1
3. Fix CustomStackTrace for rnn group

For example:
layer.printer(input=[x, y], format="x=%s y=%s")

No longer need to use SubsequenceInput. The framework will detect.

It seems that is not used.

* Also test std::vector
* Use std::vector to PadConf

RecurrentLayerGroup for training.