Distinguish between startPwm and minPwm

[markusressel]

For most fans there is a difference between

• the min pwm at which the fan starts to rotate from a stand still
• and the max pwm at which the fan still rotates when it was rotating previously

where the latter is smaller than the former in most cases.

To be able to securely make a fan start up, we need to know the startPwm value.
To also be able to let the fan run at a lower speed than startPwm (which might be possible or not) we also need to know the minPwm value.

Alternatively we could simply "jumpstart" fans by setting them to 100% for a brief moment, but this would also require knowledge about how long to do this without inducing annoying "ramping" sounds.