Apple notarization must be passed and app bundle must be signed

Apple will restrict running non-AppStore software on Macs from February 2019 unless it has passed 'notarization'.

Ideally, travis-ci should be used for automatic sending of binaries to Apple on new releases, as it can only be done from OS X.

Apple has provided this info:

"You can notarize and sign from the terminal on a Mac (using codesign and xcrun altool) or by ssh’ing into a Mac."

https://developer.apple.com/documentation/xcode/notarizing_macos_software_before_distribution/customizing_the_notarization_workflow?preferredLanguage=occ