Update wfm stitching notebook with new frame finding and time overlap removal

[nvaytet]

• We use the more general frame finding approach used in the DREAM choppers setup to find the individual WFM frames.
• We also introduce removal of time overlap between frames, by gradually increasing percentile cutoffs on the tofs of consecutive frames.
• In the process, we also added individual ids to the neutrons in a source, which are useful and used in this example.

Depends on #51

[nvaytet]

I'm converting to a draft as I think we should go with the simpler approach of computing wavelengths using interpolation which gives wavelength as a function of time of arrival.

[nvaytet]

Superseded by #57