Summary:
1. add net gradient check to dper2 model unittest framework
2. add net gradient check to mtml model
3. refactor the code setting defaults to namedtuple.
Reviewed By: kittipatv
Differential Revision: D4897169
fbshipit-source-id: 4f17dd06ee169aa1158f12f5156614d45d7d97c1
Summary: this is useful to test rnn cells
Reviewed By: dzhulgakov
Differential Revision: D4720641
fbshipit-source-id: baa7df43357ed8af72ede64be3e0a642a40472df