VBat calibration & output only PWM validation

[pkendall64]

Adds new hardware configuration validation

• "pwm_output_only" flag
• "vbat_cal_min/max" for the calibration wizard
• multiple voltage sources, vbat, vsrc1-3 including no_reading value

Updates all the existing targets to include the calibration values from the web sites and from previous known good values.

[CapnBry]

Oh hey, nice! I just assumed we'd leave the older hardware the same and the user would pick their own endpoints if they wanted to calibrate, but this is even better.

Can you verify my one comment where the atten was changed?

I will note that the ER6 and ER8 calibrations were done with a 300 point least-squares fit calibration to minimize error across the entire range and not just 2 end points, but I think the values are close enough that both are fine.