Conv kernel shapes not inferred

[rzig]

Describe the bug
remap_node_with_kernel_shape requires kernel_shape to be present. Per the ONNX docs this should be inferred when not present. remap_node_with_kernel_shape does not implement inference, causing some properly formed ONNX models to fail parsing.

To Reproduce

1. Generate an ONNX file using the Pytorch tutorial
2. Call parse_onnx on the model.

Expected behavior
The kernel shape should be inferred.