Fairy lights: separate scenes into a select entity.
Scenes require color_mode to be set to "scene", but if we add an "effect" dp,
extra values from color_mode are not selectable as effects.
Instead of putting scene as effect, separate it into its own select entity and
let the additional color_mode show through as effects.
Add the timer as a number entity instead of just an attribute. It seems
an entity with only optional dps still works.
Issue #309