I have modified the ETM suspension models to include a schmidt triggering block, so that we can choose between using the high gain low power Thorlabs PD and the low gain high power QPD. 

The Thorlabs high gain PD signal is used as the signal to trigger on, so we need to put appropriate thresholds in.

If things are "triggered", that will imply that the Thorlabs PD is seeing a lot of power, so we should be using the QPD SUM channel instead.  There is a "choice" block after the trigger block, to do this switching.

Since the LSC model will only see the output of this choice block, the gain that is currently in C1:LSC-TR[X or Y]_GAIN should be moved to the end SUS model.  We also need to find the correct gain for the QPD sum channels so that they are also normalized to "1" for single arm full power so that we can smoothly go between the 2 diodes.

Rana has promised to make screens, and write scripts for the switching stuff.