Remove read-only markers from tray application

The tray application is display-only and doesn't allow users to change
any settings. Therefore, showing (read-only) markers doesn't provide
value since all fields are implicitly read-only in this context.

Changed to_string_with_readonly_info() back to to_string_with_padding()
for the tray display.

Addresses PR #14 review comment from @LennardKittner

src/status_tray.rs

@@ -23,7 +23,7 @@ impl TrayHandler {
                 device_state.device_name.clone(),
             ),
             Some(true) => (
-                device_state.to_string_with_readonly_info(0),
+                device_state.to_string_with_padding(0),
                 device_state.device_name.clone(),
             ),
         };