Improve auto update

[albireox]

The auto update design should look more like the standard macOS experience. I don't think there's a package to do that.

When an update is available retrieve and show the change log

Keep a list of skipped versions and do not offer the update for those except when checking for updates manually.

If no update is available, show something like.

(although the current dialog is not bad).

When installing an update, show a dialog with a progress bar and the option to cancel. When the download is complete, change the button to install and restart.

Automatically check for new version when Boson starts and then every 6 hours.