Add iic mechanism wrapping the peculiar HgCd lamp sequencing

HgCd exposures are currently done by manually starting the lamps, waiting for them to warm up, then taking the exposures. This should be wrapping by iic.

Turns out the current scheme is not quite OK. With HgCd the prepare command does turn on the lamp, but if you do not send go or go noWait the lamp will be turned off after the internal wait for the go command (currently 400s), and not when the requested time expires.

If you are wrapping all of this (and I think you should) I would run:

prepare hgcd=300 # or whatever
waitForReadySignal # 120-140s

# Then either
go noWait # Returns immediately
# or
go # Returns after your requested 300s

   # take exposes in here

stop # if you use {{noWait}} or actually stop the lamps. This will update the lamp times and status for the GUI, etc.