Created by: hutuxian

Refine PaddleBox Framework：

• Add MetricMsg util class, which can calculate metrics like AUC, bucket_error, COPC.
• Replace FeedPass with new interface: BeginFeedPass & EndFeedPass
• Refactor Pull/Push Sparse Function in box_wrapper.
• Use CUDA Kernel to copy keys and copy feasign between tensor and boxps struct.
• Cache copied keys in pull sparse in order to reuse it in push period.