Make use of LightCall::from_light_color_values for restoring state

[mmakaay]

I currently make use of the RTC state store to restore state. This method works, but is not very clean code-wise, because I need to redefine a struct in my code for decoding the RTC data.
I ran into the LightCall::from_light_color_values() method, which might make things a lot cleaner.

With the current_values of the light output, I can store the active state.
With code like this, I can restore the state:

auto call = the_light.make_call();
call.from_light_color_values(id(global_var));
call.perform();