Some small improvements

[marcelveldt]

Hi, first of all great work on this, think its will be valuable to a lot of people.

May I suggest a few improvements in this PR:

• Stop running an existing dynamic scene when you start one for given entities
• The original Hue color schemas define both xy and colortemperature for non-colorlights. As the presets only contain the xy colors I've added a small converter to convert the xy color to the nearest color temperature for these cases.
• Use a short transition when starting a dynamic scene and use the configured transition time only for the subsequent loops
• Ignore a broightness of "0" as well as "None"
• Stop running a dynamic scene as soon as the lights power off --> although this needs a bit more work to clean up the remaining task.

[Hypfer]

Thanks!