Switch to Alerter for macOS

[mkozjak]

Now that Alerter is back in action again and with terminal-notifier basically not working with Tahoe moving forward (and not being updated in years), I guess we should switch to Alerter as primary choice.

I am using this library via slk.

alerter is just a split project from terminal-notifier with support for actions. It also appears not to be maintained.
Well, the support is here; if they managed to fix it, good. NSUserNotification they are using is now deprecated, and UNUserNotification should be used instead.

Originally posted by @gen2brain in #41

[gen2brain]

Yes, that looks like a much better alternative to the now-defunct terminal-notifier that does nothing better than plain osascript. As I remember, the old method bundled .app and called that instead. This is now in Swift and is using a fake bundle ID from the Terminal app. And again, private methods for images, but if it works, of course, it is better. Someone just needs to test everything, map arguments if there are big changes, and replace the current checks for terminal-notifier. I will get to that sometime, eventually, but PR is welcome.

[mkozjak]

Ended up not being as easy as just changing one program to another. More info in the PR.