Software update checks

[bartfeenstra]

Definition of Done

• Deploy an authoritative list of all Betty releases
• Have Betty, if it is run as a packaged release, periodically check this list for updates
• Notify users of updates in the CLI. Can we do this asynchronously, yet make sure the output does not get lost among all the other async output?
• Notify users of updates in the GUI
• Add a hash to the request so we can track unique installations anonymously (maybe a follow-up?)
• Add a flag to the CLI to prevent update checks.