Expose per-detector FEE voltage configuration.

The detector voltages for the different modes (idle, erase, wipe, integrate, readout) have been loaded into FEE NVRAM essentially once, when first building up the signal chain. And since there is a great deal of duplication between modes it is expressed in code. 

With the r3 problem that should be probably redone, or at least there should be a command for changing individual voltages in individual modes. That latter would be easy in the immediate term.