Send fan-mode over dbus. Fix multizone dbus command

Closes issue #7

rog-core/src/error.rs

@@ -0,0 +1,10 @@
+use std::fmt::Debug;
+use thiserror::Error;
+
+#[derive(Error, Debug)]
+pub enum RogError {
+    #[error("unable to parse string to fan mode")]
+    ParseFanLevel,
+    #[error("mode not supported")]
+    NotSupported,
+}