[CSL-677] Optimize DataMsg StakeholderId GtMsgContents serialization
[CSL-677] Optimize DataMsg StakeholderId GtMsgContents serialization

input-output-hk/cardano-sl,input-output-hk/pos-haskell-prototype,input-output-hk/cardano-sl,input-output-hk/pos-haskell-prototype,input-output-hk/cardano-sl,input-output-hk/cardano-sl,input-output-hk/pos-haskell-prototype