Sign and "notarize" Mac OS X Nmap builds

Apple has been encouraging us to obtain a Developer ID and signing key, sign our builds, and then submit them to Apple for their new "notarization" process. Apple says that "On macOS 10.14, Gatekeeper will highlight that your apps have been notarized by Apple. In an upcoming release, Gatekeeper will require notarization by default for all Developer ID apps." More details on Notarization are at https://developer.apple.com/documentation/security/notarizing_your_app_before_distribution and they have a FAQ on common notarization issues at https://developer.apple.com/documentation/security/notarizing_your_app_before_distribution/resolving_common_notarization_issues?language=objc.