Fit minimum value for SLDO to pass

Closes #163 (closed) analysis.py is upgraded, now a linear fit is performed to extrapolate the current for which the minimal shunt current criteria is passed. Moreover, the linear fit is plotted in the end. The x-axis range is now common among the three plots. Example II plot below. The dotted lines indicate the input current IinA and IinD for which the minimal IshuntA or IshuntD is passed according to the cut files.

The latest commit also Closes #164 (closed)