Add battery level to web UI

daemon/src/error.rs

@@ -15,4 +15,10 @@ pub enum RayhunterError {
     QmdlStoreError(#[from] RecordingStoreError),
     #[error("No QMDL store found at path {0}, but can't create a new one due to debug mode")]
     NoStoreDebugMode(String),
+    #[error("Error parsing file to determine battery level")]
+    BatteryLevelParseError,
+    #[error("Error parsing file to determine whether device is plugged in")]
+    BatteryPluggedInStatusParseError,
+    #[error("The requested functionality is not supported for this device")]
+    FunctionNotSupportedForDeviceError,
 }