Advanced light group control

[jseidl]

This is for tracking pending work from @caphm's PR #101. These are all awesome ideas and should be fairly easy to port now that 3.0.0 is done and stable (so far!)

The behaviour if there are already some lights in the group turned on is as follows (in the order listed):

If there are parameters given to the call to the turn_on service, the group will only act on the lights that are already turned on. This allows to change brightness, color and other attributes of turned on lights without turning on additional lights.
If the area is in sleep mode, sleep lights are turned on
If there are no overhead lights on (e.g. only accent or task lights), the overhead lights are turned on. This allows you to turn on the overhead lights when only your desk lamp is on without having to specifically specify it.
You can checkout a detailed behaviour chart here: https://docs.google.com/spreadsheets/d/106aUjxl3eox7chds_P7xT2Tiu7t7UltkIwGIKMoi0QI/edit?usp=sharing

[jseidl]

I think this PR #354 closes up materializing all of @caphm's ideas. Thank you so much and let me know if I missed anything. I didn't implemented in exactly the same way but all the concepts should be there now!