add dimming for lights

[hermannsblum]

As discussed:

the dimming of the lights could be solved similarly to that of the media players and the various sources. (maybe then only 2 elements per row but with extra dimming steps) Otherwise this is already a good stand.

Originally posted by @LasseRheinstroem in https://github.com/hermannsblum/kindle_infoscreen/pull/20#issuecomment-654257148

Alternatively, could dim by sliding up and down over a switch element.

[LasseRheinstroem]

That sounds great if it is possible, but presets are also not bad. Maybe we could implement both