Verify that APS PLL is locked in init.

--BRJ and CAR
Better fix for box car index problem.

--BRJ
Fix imaginary plots

imag(nan) = 0, but imag(complex(nan,nan)) = NaN. So, explicitly
construct data.mean as complex.
--BRJ
Evaluate electrical delay fit using polyval

--BRJ
Merge branch 'develop' of github.com:BBN-Q/Qlab into develop