Improve schedule load, add slice_like (#1299)

nnvm/include/nnvm/top/tensor.h

nnvm/python/nnvm/frontend/mxnet.py

nnvm/python/nnvm/top/nn.py

nnvm/python/nnvm/top/transform.py

nnvm/src/top/elemwise_op_common.h

nnvm/src/top/tensor/transform.cc

nnvm/tests/python/compiler/test_top_level4.py

topi/python/topi/generic/nn.py

topi/python/topi/nn/conv2d.py

topi/python/topi/x86/conv2d.py

topi/tests/python_cpp/test_topi_transform.py