Updates include plots & uncertainty checks

Sigcal no longer includes sensitivity points originating from files with
greater than 15% deviation between integral & derivative calculations.
It also spits out a plot of the sensitivity curve. Displaycal is a
quickie hack of sigcal that doesn't process, but simply opens the output
file to display the sensitivity curve. Calconst.py is the source code
for the generation of the calibration control file. It is run after the
user has calculated the damping ratio , ADC cal constants, Laser cal
constant, and free period oscillation frequency.