Improve idemix performance on HLF

Hello,

with @adecaro we identified some improvments task to provide better performance on the overall HLF transaction workflow when using idemix. I open that issue to keep track on them and see when such tasks can be implemented.

@adecaro : can you help to define here the different idemix improvments to be reported on HLF stack (crypto lib update, marshaling issue, ... ?). Thank you :)