add Topology to handle actions on network

fix parameters.append_gradient_machine

append_gradient_machine should append __gradient_machines__ in all conditions.

Add MovieLens DataSet

Feature/cifar dataset

implement more layers in v2

convert mixed layer, projection and operator

Add metric(like Error rate) to Trainer::event.

Data Feeder

MNIST dataset reader implementation

LayerOutput for single machine multiple devices

add optimizer in v2