#172, #314, #328, #378: Implement display option for membership and cert commands

• tx: monkeypatch.setattr(module, method)
• #172 (closed): Rename transaction_confirmation to gen_confirmation_table
• #172 (closed): Refactor tx confirmation, by using click.confirm()
• cert: Split pre-checks and docs gen into f()
• #314: cert: Implement display option
  • The generated document is displayed
  • In case the option is passed, display the table and
  • the generated document
• #314: membership: Implement display option
  • Add ability to send the doc after displaying the doc
  • Do not by-pass the license approval
  • Issuance approval after confirmation and doc display
  • Set one confirmation prompt after the table and the document displays
  • Use dry-run global option
  • Add test for the display option
• #314: Add global --display/-d and --dry-run/-n options
  • display option to display the generated document before sending it
  • Move dry-run option as a general one
  • Add error handling to have dry-run and display options together
  • Test when display and dry_run options are passed together
• #378: Create and use generic send_doc_confirmation() in cert and membership commands
• #328: cert/tx: Import top-level Click module
• #328: Import directly tui module for cert, membership, tui (constants)