This PR installs and enables versioneer to manage version strings in a more automated way.

Because Versioneer gathers its version-related information from the local git repo, naturally, it does not support frozen interpreters/installations, so this PR also updates the PyInstaller ".spec" file to write the current version string to a version.txt file in the resources dir (and modifies __init__.py to load the version string from that file at startup in the event that the application is running frozen).