Effectively flips all values related to the directionality of current
through the TEC, including current maximums. The reversed status is
stored in the flash store and will be loaded on reset once saved.
The command is "pwm <ch> polarity <normal/reversed>", where the "normal"
polarity is indicated by the front panel markings.
This is needed for IDC cable connections to the Sinara 5432 DAC
"Zotino", since the TEC pins of the 10-pin connector on the Thermostat
and Zotino have opposite polarities.
