Ml/siglent rework2

[mileslucas]

Continuation of #290 without git issues.

[mileslucas]

This has critical bugs in the ttmModulator app. The trace roughly goes like

1. after pressing modulate, modwfs thinks fxngenmodwfs has timed out because it is waiting for the fxngen C*amp voltage to reach the set point but it never does
2. The voltage target is not reached in fxngenmodwfs because of the check that the fxngen is within the 0-10V range
3. This is because the C*ofst is not updated to be a positive value, ergo the sine wave is negative, not between 0-10V
4. modwfs is supposed to send a new C*ofst target, but this code is never called--throwing a print inside the indi callback on the fxngenmodwfs offsets never prints.

Now, I suspect this might have to do with the way the indi properties are set up in modwfs. Rather than having two separate properties for each fxngen parameter (one listening for the current value, and one used for sending the target value), but I haven't confirmed that. If so, the correct approach would a bit of a more significant rewrite of modwfs, rewriting the entire indi property logic.