Background service (#43)

better handling of background-service: lan-mouse can now be run without a gui by specifying --daemon as an argument.
Otherwise the servic will be run as a child process and correctly terminate when the window is closed / frontend exits.

Closes #38

src/backend/consumer/windows.rs

@@ -1,4 +1,3 @@
-use anyhow::Result;
 use async_trait::async_trait;
 use crate::{event::{KeyboardEvent, PointerEvent}, consumer::EventConsumer};
 use winapi::{