Created a Dark Mode CSS

Hi, OK now.
I notice you changed

1. SamplerBox.css 
   
2. SamplerBox_GUI.js
   
3. lcdmenu.html
   
4. readme.html
   

First is obvious 
3rd and 4th are done in screens not expecting much future updates.

With 2nd I foresee future issues, as the API will have changes when new functions are added (which I definitely plan to do - actually doing already).
As it is for the lcdmenu only, I'll have a look whether I can change the js and html in such a way that your change can be limited to the html.

I'll send you a PM when the result is on the download pages, so you can check the result.
Thanks for your contribution!
Hans