Add optional system notifications in example CLI

[nanu-c]

This pr adds notifications via a generic rust library

[nanu-c]

Question, there is no easier way to get my uuid, because whoami() is asking signal server not? And i didn't use manager.get_contact_by_id(uuid) because it's broken and throws always a Error: JsonError(Error("invalid type: map, expected a sequence", line: 1, column: 0))

[nanu-c]

I found the uuid, but i would recommend to rename it to my_uuid. I have update the pr accordingly

[gferon]

I feel like we should find a way to put this inside of Manager since IMO this is what presage is about. I'm fine merging this as-is for now, though. I'll try to see if there's a way to include it inside.

[nanu-c]

I agree, but it should be optional, because maybe it's used on a headless server without the need for notifications. I can resolve the fmt and build problems

[nanu-c]

I have to test if typing messages etc. also trigger a notification. And we should find a way to toggle the notifcations per session.

[gferon]

I ended up rewriting the message receiving part of the CLI to format messages in a much prettier fashion. Thanks for the PR!