[TASK] Add balance_change array to transaction response, computed from metadata

"Meta-metadata is specifically filtered from transaction submission response." - This doesn't appear to be true currently. The fixtures were generated from the transaction submission response and contain all the metadata.

"if you add your changes to the Meta class this step would be unnecessary" - Why would this be unnecessary? The spec says ripple-lib should "return" a balance changes array; doesn't it need to be in the response message to be returned?