Close the client in case of a negative answer to the confirmation

Address issue from !112 (closed)

• [fix] Close the client in case of a negative answer to the confirmation
  • for tx and cert commands
• [enh] Introduce exit status constants

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Note: You can review this change. If it actually fix the issue, is correctly implemented and does not introduce new bug, tell me if you approve it. Then I will merge it.

changed milestone to %0.8.0

added API: BMA Bug CLI D: Certification D: Transfer Network labels

added enhancement label

mentioned in merge request !114 (closed)

resolved all threads

merged