SINGA-410 Add two function, set_params() and get_params(), for Autograd Layer class
SINGA-410 Add two function, set_params() and get_params(), for Autograd Layer class

- modified code design.

apache/incubator-singa,nusdbsystem/incubator-singa,nusdbsystem/incubator-singa,ijingo/incubator-singa,apache/incubator-singa,ijingo/incubator-singa,nudles/incubator-singa,ijingo/incubator-singa,kaiping/incubator-singa,nusdbsystem/incubator-singa,kaiping/incubator-singa,ijingo/incubator-singa,kaiping/incubator-singa,nudles/incubator-singa,ijingo/incubator-singa,apache/incubator-singa,kaiping/incubator-singa,kaiping/incubator-singa,apache/incubator-singa,nusdbsystem/incubator-singa,nudles/incubator-singa,nusdbsystem/incubator-singa,nudles/incubator-singa,nudles/incubator-singa,apache/incubator-singa