Add smartdevice module for led controls (#761)

Allows controlling LED on devices that support it.

kasa/smart/modules/__init__.py

@@ -3,6 +3,7 @@ from .childdevicemodule import ChildDeviceModule
 from .cloudmodule import CloudModule
 from .devicemodule import DeviceModule
 from .energymodule import EnergyModule
+from .ledmodule import LedModule
 from .lighttransitionmodule import LightTransitionModule
 from .timemodule import TimeModule
 
@@ -11,6 +12,7 @@ __all__ = [
     "EnergyModule",
     "DeviceModule",
     "ChildDeviceModule",
+    "LedModule",
     "CloudModule",
     "LightTransitionModule",
 ]