Entity registry (#11979)

* Entity#unique_id defaults to None

* Initial commit entity registry

* Clean up unique_id property

* Lint

* Add tests to entity component

* Lint

* Restore some unique ids

* Spelling

* Remove use of IP address for unique ID

* Add tests

* Add tests

* Fix tests

* Add some docs

* Add one more test

* Fix new test…

homeassistant/components/binary_sensor/hikvision.py

@@ -212,7 +212,7 @@ class HikvisionBinarySensor(BinarySensorDevice):
     @property
     def unique_id(self):
         """Return an unique ID."""
-        return '{}.{}'.format(self.__class__, self._id)
+        return self._id
 
     @property
     def is_on(self):