Use contract spec to annotate errors in invocation

[leighmcculloch]

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What problem does your feature solve?

When a contract invocation fails the client outputs the contract error as a number, such as 5, or 22.

The developer has to manually go to the contract spec to find out what error that code maps to.

What would you like to see?

The cli use the spec to map to the error name and output the error name alongside the error code.