Fix S-Curve analysis
This MR addresses #91 (closed), #73 (closed) and adds:
- Enhanced convergence of S-Curve fit from 75% to above 99% using proper fitting with start values and errors
- Bugfix threshold scan unit test
- Chi2/ndf plot
- Masking pixels with failed S-Curve fit in Threshold/Noise Plot
Edited by Michael Daas