Add: On device Claibrated He Level Display

[Bilchreis]

Currently Levelmeters display the He level only as a mapping from the measured fill height in % to the volume of the Vessel. On thge serverside a proper calibration using a lookup table is already implemented.

Sometihng similar is needed for displaying corrected He levels on the device itself.

The LUT:

• 11 entrys
• steps for 0% -100% in 10% steps
• this means ther will be 10 bins for interpolation

Interpolation:

y_LevelCal = y_1 + (x_LevelMeasured - x_1) *  (y_2 - y_1) / (x_2 - x_1)

example lut:

Level	Vessel Vol
0%	10L
10%	20L
20%	30L
30%	60L
40%	90L
50%	120L
60%	150L
70%	180L
80%	190L
90%	200L
100%	210L

• Sending the LUT from the Server will necessetate a new message code
• it will be sent some time during startup
• LUT will be saved in EEPROM
• LUT functionality can be enabled in Options (external pressure sensor option can be removed)