[FR] Add wizard or single slider to control case lights

[WheresWaldo]

Feature Request

What is the feature?

Add a screen or wizard to control case lighting for Robo Mainboard 1.1.8 and firmware version Marlin 1.1.6 / Robo 1.2.1

Why this feature?

It is there in the new hardware and enabled in firmware, now people need an easy way to control it besides adding the appropriate G-code to scripts.

Easy to do just add a slider control that can be set from 0 - 255 and a variable to read where it is set, a button to turn the lights on using M355 S1 Pnnn where nnn is the number from the slider. Because of a bug in Marlin 1.1.6 you need to turn the brightness to 0 so the off button should be M355 S1 P0 instead of the normal M355 S0.

[AllenMcAfee]

@WheresWaldo We will add this to the roadmap!