create light.hue_activate_scene service (#4425)

* create light.hue_activate_scene service

This creates a light.hue_activate_scene service that takes group_name
and scene_name, and calls phue's bridge.run_scene with those
parameters. This allows calling hue bridge stored scene names by name
during automation.

This only currently works reliably in 1 hue hub configurations (which
is most of them). Phue will be further enhanced to display warnings
when it can't figure out what to do with the parameters passed in to HA.

* Update hue.py