Allow input capture & emulation being disabled (#158)

* Input capture and emulation can now be disabled and will prompt the user to enable again.

* Improved error handling to deliver more useful error messages

input-emulation/src/macos.rs

@@ -295,4 +295,6 @@ impl InputEmulation for MacOSEmulation {
     async fn create(&mut self, _handle: EmulationHandle) {}
 
     async fn destroy(&mut self, _handle: EmulationHandle) {}
+
+    async fn terminate(&mut self) {}
 }