* Enable brightness slider for RGB
If we are using RGB with no brightness topic, the brighness slider
should still be visible, as we can scale the RGB amount to give us the
brightness.
* Output RGB scaled by brightness
If we are outputting to an RGB device, but do not have a dedicated
brightness topic set, when the brightness slider is changed, we should
output the current colour's HS, with the V coming from the brightness
slider.
* Brightness from RGB when we're not using a brightness topic
When we aren't using a brightness topic, set the brightness slider based
on the received value from an RGB -> HSV conversion.
* Test for new brightness state scaled by RGB
This adds a test to make sure the brightness stored in the state is
being computed correctly from the RGB value when a dedicated brightness
topic is not set.
* Changes from review
Fixes formatting of supported features flags, and checks HS colour
hasn't been set when operating in RGB-only mode
* Set optimistic brightness correctly in rgb mode
When we're using rgb mode to set the brightness, we want to set
optimistic brightness if:
we are running in optimistic mode
OR
the brightness state topic isn't set and we have a brightness command topic
OR
the rgb state topic isn't set and we don't have a brightness command topic
* Add test for turn_on in RGB brightness mode
2e973c7572