Signature feature should generate cleaner signatures

[agibsonccc]

Issue Description

We often define a single op multiple times, because it can take some variables as either args or tensors.
T signature feature (https://github.com/eclipse/deeplearning4j/blob/master/contrib/codegen-tools/codegen/README.md#signature) should actually take care of that more cleanly.

Please describe our issue, along with:

• expected behavior
• encountered behavior

Version Information

Please indicate relevant versions, including, if relevant:

• Deeplearning4j version
• Platform information (OS, etc)
• CUDA version, if used
• NVIDIA driver version, if in use

Additional Information

Where applicable, please also provide:

• Full log or exception stack trace (ideally in a Gist: gist.github.com)
• pom.xml file or similar (also in a Gist)

Contributing

If you'd like to help us fix the issue by contributing some code, but would
like guidance or help in doing so, please mention it!