* Add a group notify platform which allows sending a single notification to multiple platforms.
* Correctly sort group.py
* Clean up the payload logic
* Make name and entity id required in the schema
* Deep update the dictionary to fix a bug where data wasnt merging.
* Add notify.group tests.
* Improve docstrings.
* Change entities to services and entity_id to service
* Make service a slug without a default value
* Update tests for entities->services, entity_id->service
* vol.Any(cv.slug) -> cv.slug
Paulus Schoutsen
Fabian Affolter
Pascal Vizeli
Robbie Trencheny