This adds a 'sensor_class' property and attribute, which should be either
None or one of several defined SENSOR_CLASSES to indicate contextual
information about what the sensor is measuring.
This allows you to get every door, window, smoke, etc zone from your security
panel into HA. This uses the live eventing feature of pynx584, which means you
get instantaneous signaling into HA when a door opens or something happens,
which is handy for automating lights on when doors open after dark, etc.
Requires update to pynx584 0.2
