This PR adds make-targets/scripts to better support and partially automate the newly-enforced macOS "notarization" process (as required by Apple for all newly signed applications beginning in January 2020).

Two basic Vagrantfiles are also included to help facilitate the provisioning of macOS "Mojave" (10.14) and "Catalina" (10.15) environments so that future "notarized" builds/releases can be tested across operating systems that are still (currently) supported by Apple.

Closes #261