[TOP] Add dense, batchnorm (#22)

nnvm/include/nnvm/compiler/op_attr_types.h

nnvm/python/nnvm/compiler/build_module.py

nnvm/python/nnvm/compiler/registry.py

nnvm/python/nnvm/top/__init__.py

nnvm/python/nnvm/top/nn.py

nnvm/python/nnvm/top/tensor.py

nnvm/python/nnvm/top/transform.py

nnvm/src/compiler/graph_fuse.cc

nnvm/src/compiler/packed_func_ext.cc

nnvm/src/compiler/simplify_batch_norm.cc

nnvm/src/pass/print_graph_ir.cc

nnvm/tests/python/compiler/test_simplify_batchnorm.py

nnvm/tests/python/compiler/test_top_level1.py

nnvm/tests/python/compiler/test_top_level2.py