* Add MySensorsDeviceEntity class to hold the common attributes,
properties and methods for mysensors entities.
* Inherit from MySensorsDeviceEntity class in binary_sensor, light,
sensor and switch mysensors platforms.
* Remove not needed attribute and method for const in GatewayWrapper
class. The const attribute is already set in the wrapped object.
* Clean up state property for mysensors sensor entities.
* Inherit from MySensorsLightRGB in MySensorsLightRGBW class.
* Remove use of get_component in mysensors component and platforms.
* Clean up update method in MySensorsDeviceEntity class.
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