Fix circular import, add test survey action, add interpolated values to calibration files

[jhazentia]

• Fixes circular import issues by moving signals.py and removing gps import from scos_actions hardware
• Adds test survey iq action
• Adds interpolated values for USRP actions and test actions to the example calibration files

[aromanielloNTIA]

Looks good! See a couple small comments. With a refactoring change like this it may also be worth another quick pass through the code (or search-through using your IDE) to check for any references to the changed imports (signals, gps) that might have been overlooked (they wouldn't show in the diffs).

Another thing to consider is that there are a few places here where MockGPS() is passed as a default argument. The MockGPS instance is technically a mutable object. Based on the definition of the MockGPS, I wouldn't expect this to cause any issues as it is currently implemented. However, if the GPS interface is ever expanded and changed significantly in the future, this could lead to unexpected behavior that's hard to track down. A suggested fix would be replacing instances like:

def some_function(parameter=MockGPS()):
    do_something(parameter)
    ...

with

def some_function(parameter=None):
    if parameter is None:
        parameter = MockGPS()
    do_something(parameter)
    ...

[aromanielloNTIA]

All my previous comments have been addressed. I also think the addition of logger warnings for the mock sigan/gps are great additions.