Add common energy module and deprecate device emeter attributes (#976)

Consolidates logic for energy monitoring across smart and iot devices.
Deprecates emeter attributes in favour of common names.

kasa/iot/modules/led.py

@@ -30,3 +30,8 @@ class Led(IotModule, LedInterface):
     async def set_led(self, state: bool):
         """Set the state of the led (night mode)."""
         return await self.call("set_led_off", {"off": int(not state)})
+
+    @property
+    def is_supported(self) -> bool:
+        """Return whether the module is supported by the device."""
+        return "led_off" in self.data