Level app: coloration of RxSat value

[gullradriel]

That PR add a coloration of the whole "RxSat: XXX%" string, with the following rules:

• 80% of sat is the ideal value
• RxSat <= 80 => gradient from (rxSat 0,red) to (rxSat 80,green)
• RxSat > 80 => gradient from (rxSat 80,green) to (rxSat 100,red)
  ## Screenshots
  

[NotherNgineer]

Approved with a few minor comments: The blue is a little hard to see (without any R & G mixed in for brightness), and I might suggest moving the "percent to color gradient" calculation code to its own function.

[gullradriel]

Okay, I changed the way it's displayed.
That's the best I got:

[gullradriel]

"percent to color gradient" calculation code to its own function => we may need generic ones like in P5.js
I'm keeping the idea under the hat