Latch some (at least ENU shutter) header info while integrating

Most header info is latched right after wipe has finished and integration started. But note that this is before the shutters are opened and most lamps turned on. We play a game so that we get the commanded lamp states (from DCB and later pfiLamps), but not measured currents. We do not even do that for the shutters: the ENU W_ENSHUT value is always "close"

Think out what we actually want and can safely provide. We want to do this right for bias, 1-second calibration exposures, and "long" exposures.