Remove default power-cycle and initialization from ASIC/H4 startup

SAM/ASIC/H4 initialization is by default done completely every time: we power-cycle the whole thing and initialize the same way every time, configuring the QuickUSB-mapped registers on the SAM, downloading the SAM/Jade image, powering up and enumerating the ASIC bus, downloading the ASIC image and starting the ASIC main loop, and finally loading ASIC and H4 configuration registers and forcing an ASIC reconfiguration. Basically, this is a copy of what the Teledyne software did.

But the power-cycle and bias voltage adjustments affect the detector in various ways, especially persistence: power-cycling the ASIC and H4, setting some default DSub and VReset values in the boot image, then setting them immediately after can flood the detector.

Switch to (or at least default to) a startup sequence which assumes that the DAQ chain is still working. This may be tricky.