Change Dict attributes scope from private to protected
Change Dict attributes scope from private to protected

Former-commit-id: 5edd23ef430fb57d621d8e1c400dec9f0c934cb2
shuheik/dynet,chunyang-wen/dynet,shuheik/dynet,clab/dynet,xunzhang/dynet,chunyang-wen/dynet,clab/dynet,clab/dynet,clab/cnn,danielhers/dynet,xunzhang/dynet,clab/dynet,shuheik/dynet,clab/cnn,clab/cnn,danielhers/dynet,shuheik/dynet,shuheik/dynet,xunzhang/dynet,shuheik/dynet,danielhers/dynet,chunyang-wen/dynet,shuheik/dynet,clab/dynet,danielhers/dynet,xunzhang/dynet,danielhers/dynet,danielhers/dynet,clab/dynet,danielhers/dynet,chunyang-wen/dynet,clab/dynet